Reintroduce install instructions to docs

This is mostly a copy of the install from source instructions from
https://buildstream.build/install.html.
Edits have been made to focus more on Buildstream 2.
Sections for tarball installation and package installation have
been removed, as they cannot currently be used for BuildStream 2.
Docker section has been moved to the docker-image repository.
Docs have been reduced down to a single page.

2 files changed, 385 insertions, 0 deletions

diff --git a/doc/source/index.rst b/doc/source/index.rst
index 4d4e24ac2..68b13dab4 100644
--- a/doc/source/index.rst
+++ b/doc/source/index.rst
@@ -17,6 +17,7 @@ Later sections provide detailed information on BuildStream internals.
    :maxdepth: 1
 
    main_about
+   main_install
    main_using
    main_core
    CONTRIBUTING
diff --git a/doc/source/main_install.rst b/doc/source/main_install.rst
new file mode 100644
index 000000000..c715b818f
--- /dev/null
+++ b/doc/source/main_install.rst
@@ -0,0 +1,384 @@
+Installing
+==========
+
+Until BuildStream is available in your distro, you may need to install
+it yourself from source. The necessary steps are:
+
+* :ref:`Install dependencies<install-dependencies>`
+* :ref:`Install BuildBox<install-buildbox>`
+* :ref:`Install BuildStream<install-buildstream>` (from a git checkout, or from PyPi)
+* :ref:`Update PATH<post-install>`
+
+Alternatively, BuildStream can be run in :ref:`a container<install-container>`.
+
+
+.. _install-dependencies:
+
+Installing Dependencies
+-----------------------
+
+Before installing BuildStream from source, it is necessary to first install
+the system dependencies. Below are some linux distribution specific instructions
+for installing these dependencies.
+
+BuildStream requires the following base system requirements:
+
+- python3 >= 3.6
+- bubblewrap >= 0.1.2
+- fuse2
+- pip
+- :ref:`buildbox-casd<install-buildbox>`
+
+BuildStream also depends on the host tools for the :mod:`Source <buildstream.source>` plugins.
+Refer to the respective :ref:`source plugin <plugins_sources>` documentation for host tool
+requirements of specific plugins.
+
+The default plugins with extra host dependencies are:
+
+- bzr
+- deb
+- git
+- ostree
+- patch
+- pip
+- tar
+
+
+Arch Linux
+~~~~~~~~~~
+Install the dependencies with::
+
+
+    sudo pacman -S python fuse2 bubblewrap python-pip
+
+
+For the default plugins::
+
+
+    sudo pacman -S bzr git lzip patch ostree python-gobject
+
+The package *python-arpy* is required by the deb source plugin. This is not
+obtainable via ``pacman``, you must get
+`python-arpy from AUR <https://aur.archlinux.org/packages/python-arpy/>`_
+
+To install::
+
+
+    wget https://aur.archlinux.org/cgit/aur.git/snapshot/python-arpy.tar.gz
+    tar -xvf python-arpy.tar.gz
+    cd python-arpy
+    makepkg -si
+
+
+Debian
+~~~~~~
+Install the dependencies with::
+
+
+    sudo apt-get install \
+        python3 fuse bubblewrap \
+        python3-pip python3-dev
+
+For the default plugins:
+
+Stretch
++++++++
+With stretch, you first need to ensure that you have the backports repository
+setup as described `here <https://backports.debian.org/Instructions/>`_
+
+By adding the following line to your sources.list::
+
+
+    deb http://ftp.debian.org/debian stretch-backports main
+
+And then running::
+
+
+    sudo apt update
+
+At this point you should be able to get the system requirements for the default plugins with::
+
+
+    sudo apt install \
+        bzr git lzip patch python3-arpy python3-gi
+    sudo apt install -t stretch-backports \
+        gir1.2-ostree-1.0 ostree
+
+Buster or Sid
+++++++++++++++++
+For debian unstable or testing, only the following line should be enough
+to get the system requirements for the default plugins installed::
+
+
+    sudo apt-get install \
+        lzip git bzr patch python3-arpy gir1.2-ostree-1.0 ostree python3-gi
+
+
+Fedora
+~~~~~~
+For recent fedora systems, the following line should get you the system
+requirements you need::
+
+
+    dnf install -y \
+        python3 fuse bubblewrap \
+        python3-pip python3-devel
+
+For the default plugins::
+
+
+    dnf install -y \
+        bzr git lzip patch ostree python3-gobject
+    pip3 install --user arpy
+
+
+Ubuntu
+~~~~~~
+
+Ubuntu 18.04 LTS or later
++++++++++++++++++++++++++
+Install the dependencies with::
+
+
+    sudo apt install \
+        python3 fuse bubblewrap \
+        python3-pip python3-dev
+
+For the default plugins::
+
+
+    sudo apt install \
+        bzr git lzip patch python3-arpy gir1.2-ostree-1.0 ostree python3-gi
+
+Ubuntu 16.04 LTS
+++++++++++++++++
+On Ubuntu 16.04, `bubblewrap <https://github.com/projectatomic/bubblewrap/>`_
+or `ostree <https://github.com/ostreedev/ostree>`_ are not available in the official repositories)
+You will need to install them in whichever way you see fit. Refer the the upstream documentation
+for advice on this.
+
+
+.. _install-buildbox:
+
+Installing BuildBox
+-------------------
+
+BuildStream master now depends on buildbox-casd to manage the local CAS cache
+and communicate with CAS servers. buildbox-run is used for sandboxing. BuildBox
+components are still in development and there are no stable releases yet.
+Thus, they're not available yet in Linux distros and they have to be manually
+installed.
+
+These components can be installed from binaries, or built from source.
+
+Install binaries
+~~~~~~~~~~~~~~~~
+| Linux x86-64 users can download statically linked binaries: `buildbox-x86_64-linux.tar.xz <https://buildbox-casd-binaries.nyc3.cdn.digitaloceanspaces.com/buildbox-x86_64-linux-0.0.9-983edf11.tar.xz>`_
+| ``sha256sum 983edf113e945ab723a9ddfd4c00dd855db0175c81373dbc0ad809045e5801a3``
+
+The tarball contains the binaries ``buildbox-casd``, ``buildbox-fuse``,
+``buildbox-run-bubblewrap`` and the symlink ``buildbox-run``, which should be
+extracted into a directory in ``PATH``, e.g., ``~/.local/bin``.
+
+
+Build from source
+~~~~~~~~~~~~~~~~~
+
+Each of the 4 buildbox components can be installed separately from their
+respective git repositiories, and each respository has individual install
+instructions. Make sure that you're installing the correct version of
+each component.
+
+| **Buildbox-common:** See the installation section in:
+| https://gitlab.com/BuildGrid/buildbox/buildbox-common/-/blob/0.0.9/README.rst
+| (Be sure to install from the 0.0.9 tag.)
+
+| **Buildbox-casd:** See the installation section in:
+| https://gitlab.com/BuildGrid/buildbox/buildbox-casd/-/blob/0.0.9/README.rst \
+| (Be sure to install from the 0.0.9 tag.)
+
+| **Buildbox-fuse:** See
+| https://gitlab.com/BuildGrid/buildbox/buildbox-fuse/-/blob/0.0.8/INSTALL.rst
+| (Be sure to install from the 0.0.8 tag.)
+
+| **Buildbox-run-bublewrap:** See the installation section in:
+| https://gitlab.com/BuildGrid/buildbox/buildbox-run-bubblewrap/-/blob/master/README.rst
+| (Be sure to install from the 0.0.8 tag.)
+
+Finally, configure buildbox-run-bubblewrap as the default buildbox-run
+implementation::
+
+    ln -sv buildbox-run-bubblewrap /usr/local/bin/buildbox-run
+
+
+.. _install-buildstream:
+
+Installing BuildStream
+----------------------
+
+Installing from PyPI
+~~~~~~~~~~~~~~~~~~~~
+Once you have the base system dependencies, you can install the BuildStream
+python package as a regular user.
+
+To install from PyPI, you will additionally require:
+
+ - pip for python3 (only required for setup)
+ - Python 3 development libraries and headers
+
+
+For the latest dev snapshot of BuildStream 2, simply run the following command::
+
+    pip3 install --user --pre BuildStream
+
+This will install latest dev snapshot of BuildStream and its pure python
+dependencies into your user's homedir in ``~/.local``.
+
+.. note::
+
+   At time of writing, BuildStream 2 is only available as dev snapshots; this
+   is why the ``--pre`` option is required.  Running
+   ``pip3 install --user BuildStream`` (without the ``--pre`` option)
+   will install Buildsteam 1.
+
+You can also install a specific dev snapshot of Buildstream by specifying the
+version. eg ``pip3 install --user BuildStream==1.93.2.dev0``.
+Available versions can be found on the BuildStream history page `on PyPi 
+<https://pypi.org/project/BuildStream/#history>`_.
+Note that some of the oldest versions are not available on PyPI.
+
+Keep following the :ref:`instructions below<post-install>` to ensure that the ``bst``
+command is in your ``PATH``.
+
+Upgrading from PyPI
++++++++++++++++++++
+Once you have already installed BuildStream from PyPI, you can later update
+to the latest dev snapshot like so::
+
+
+    pip3 install --user --upgrade --pre BuildStream
+
+
+
+Installing from a git checkout
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+To install directly from the `git repository <https://gitlab.com/BuildStream/buildstream.git>`_
+using python's ``pip`` package manager, you will additionally require:
+
+- pip for python3 (only required for setup)
+- Python 3 development libraries and headers
+- git (to checkout BuildStream)
+
+Before installing, please check the existing tags in the git repository
+and determine which version you want to install.
+
+Run the following commands::
+
+
+    git clone https://gitlab.com/BuildStream/buildstream.git
+    cd buildstream
+    git checkout <desired release tag>
+    pip3 install --user .
+
+This will install BuildStream's pure python dependencies into
+your user's homedir in ``~/.local`` and will run BuildStream directly
+from the git checkout directory.
+
+Keep following the instructions below to ensure that the ``bst``
+command is in your ``PATH`` and to enable bash completions for it.
+
+
+Upgrading from a git checkout
++++++++++++++++++++++++++++++
+If you installed BuildStream from a local git checkout using ``-e`` option, all
+you need to do to upgrade BuildStream is to update your local git checkout::
+
+    cd /path/to/buildstream
+    git pull --rebase
+
+If you did not specify the ``-e`` option at install time, you will
+need to cleanly reinstall BuildStream::
+
+    pip3 uninstall buildstream
+    cd /path/to/buildstream
+    git pull --rebase
+    pip3 install --user .
+
+Installing in virtual environments
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+You can consider installing BuildStream in a
+`Virtual Environment <https://docs.python.org/3/tutorial/venv.html>`_ if you want
+to install multiple versions of BuildStream, or to isolate BuildStream and its
+dependencies from other Python packages.
+
+Here is how to install BuildStream stable and development snapshot releases in
+virtual environments of their own::
+
+
+    # Install BuildStream stable in an environment called "venv-bst-stable"
+    # (At time of writing, this will be BuildStream 1)
+    python3 -m venv venv-bst-stable
+    venv-bst-stable/bin/pip install BuildStream
+
+    # Install BuildStream latest development snapshot in an environment
+    # called "venv-bst-latest"
+    # (At time of writing, this will be Buildstream 2)
+    python3 -m venv venv-bst-latest
+    venv-bst-latest/bin/pip install --pre BuildStream
+
+To start using BuildStream from the desired environment, you will need to
+activate it first. Activating it will automatically add ``bst`` to your ``PATH``
+and set up other necessary environment variables::
+
+
+    # Use BuildStream stable from venv-bst-stable
+    source venv-bst-stable/bin/activate
+    bst --version
+
+    # Use BuildStream latest from venv-bst-latest
+    source venv-bst-latest/bin/activate
+    bst --version
+
+    # Once you are done, remember to deactivate the virtual environment
+    deactivate
+
+If you do not want to manage your virtual environments manually, you can
+consider using `pipx <https://docs.python.org/3/tutorial/venv.html>`_.
+
+
+.. _post-install:
+
+Post-install setup
+------------------
+
+After having installed from source using any of the above methods, some
+setup will be required to use BuildStream.
+
+
+
+Adjust ``PATH``
+~~~~~~~~~~~~~~~
+Since BuildStream is now installed under your local user's install directories,
+you need to ensure that ``PATH`` is adjusted.
+
+A regular way to do this is to add the following line to the end of your ``~/.bashrc``::
+
+  export PATH="${PATH}:${HOME}/.local/bin"
+
+.. note::
+
+   You will have to restart your terminal in order for these changes to take effect.
+
+
+.. _install-container:
+
+Buildstream Inside a Container
+-------------------------------
+
+If your system cannot provide the base requirements, it is possible to run
+BuildStream within a container. This gives you an easy way to get started
+using BuildStream on any Unix-like platform where containers are available,
+including macOS. 
+
+For details, see the `Buildstream Docker documentation
+<https://gitlab.com/BuildStream/buildstream-docker-images/-/blob/master/USING.md>`_