Centralize config for markdownlint

The configuration is currently only specified in CI, by moving it into
`.mdlrc` we get immediate feedback locally in supported editors.

To ensure `mdl` is available it's also added to the `Gemfile`, though
CI will still use the version installed in the `gitlab-docs-lint` image.

3 files changed, 8 insertions, 8 deletions

diff --git a/doc/ci/docker/using_docker_images.md b/doc/ci/docker/using_docker_images.md
index 816bd35018a..2d7fb323d79 100644
--- a/doc/ci/docker/using_docker_images.md
+++ b/doc/ci/docker/using_docker_images.md
@@ -530,11 +530,11 @@ There are two ways to determine the value of `DOCKER_AUTH_CONFIG`:
     ```
 
 - **Second way -** In some setups, it's possible that Docker client
-will use the available system keystore to store the result of `docker
-login`. In that case, it's impossible to read `~/.docker/config.json`,
-so you will need to prepare the required base64-encoded version of
-`${username}:${password}` manually. Open a terminal and execute the
-following command:
+  will use the available system keystore to store the result of `docker
+  login`. In that case, it's impossible to read `~/.docker/config.json`,
+  so you will need to prepare the required base64-encoded version of
+  `${username}:${password}` manually. Open a terminal and execute the
+  following command:
 
     ```bash
     echo -n "my_username:my_password" | base64
diff --git a/doc/development/documentation/styleguide.md b/doc/development/documentation/styleguide.md
index 7127efb7405..d9cea0614c3 100644
--- a/doc/development/documentation/styleguide.md
+++ b/doc/development/documentation/styleguide.md
@@ -518,7 +518,7 @@ you have your MR reviewed and approved by a technical writer.
 ```html
 leave a blank line here
 <div class="video-fallback">
-  See the video: [Video title](https://www.youtube.com/watch?v=MqL6BMOySIQ).
+  See the video: <a href="https://www.youtube.com/watch?v=MqL6BMOySIQ">Video title</a>.
 </div>
 <figure class="video-container">
   <iframe src="https://www.youtube.com/embed/MqL6BMOySIQ" frameborder="0" allowfullscreen="true"> </iframe>
@@ -529,7 +529,7 @@ leave a blank line here
 This is how it renders on docs.gitlab.com:
 
 <div class="video-fallback">
-  See the video: [What is GitLab](https://www.youtube.com/watch?v=enMumwvLAug).
+  See the video: <a href="https://www.youtube.com/watch?v=enMumwvLAug">What is GitLab</a>.
 </div>
 <figure class="video-container">
   <iframe src="https://www.youtube.com/embed/MqL6BMOySIQ" frameborder="0" allowfullscreen="true"> </iframe>
diff --git a/doc/user/project/deploy_tokens/index.md b/doc/user/project/deploy_tokens/index.md
index 5e11e7c0203..72594733cd3 100644
--- a/doc/user/project/deploy_tokens/index.md
+++ b/doc/user/project/deploy_tokens/index.md
@@ -41,7 +41,7 @@ the following table.
 
 ## Deploy token custom username
 
-> [Introduced][https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/29639] in GitLab 12.1.
+> [Introduced](https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/29639) in GitLab 12.1.
 
 The default username format is `gitlab+deploy-token-#{n}`. Some tools or platforms may not support this format,
 in such case you can specify custom username to be used when creating the deploy token.