build: add Make `doc-only` target

Allows building just docs using existing Node instead of building Node
first.

PR-URL: https://github.com/nodejs/node/pull/3888
Reviewed-By: Chris Dickinson <christopher.s.dickinson@gmail.com>
Reviewed-By: Rod Vagg <rod@vagg.org>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Myles Borins <myles.borins@gmail.com>

1 files changed, 10 insertions, 0 deletions

diff --git a/BUILDING.md b/BUILDING.md
index 7e52658eec..e9bf0bc013 100644
--- a/BUILDING.md
+++ b/BUILDING.md
@@ -67,10 +67,20 @@ $ make test-npm
 
 To build the documentation:
 
+This will build Node.js first (if necessary) and then use it to build the docs:
+
 ```text
 $ make doc
 ```
 
+If you have an existing Node.js you can build just the docs with:
+
+```text
+$ NODE=node make doc-only
+```
+
+(Where `node` is the path to your executable.)
+
 To read the documentation:
 
 ```text