docs/README: Document sphinx-autobuild for local preview.

Signed-off-by: Jos Verlinde <Jos_Verlinde@hotmail.com>

docs/README.md

@@ -24,6 +24,21 @@ In `micropython/docs`, build the docs:
 
 You'll find the index page at `micropython/docs/build/html/index.html`.
 
+Documentation autobuild
+-----------------------
+
+For a more convenient development experience, you can use `sphinx-autobuild`
+to automatically rebuild and serve the documentation when you make changes:
+
+    pip install sphinx-autobuild
+
+Then run from the `micropython/docs` directory:
+
+    sphinx-autobuild . build/html
+
+This will start a local web server (typically at `http://127.0.0.1:8000`)
+and automatically rebuild the documentation whenever you save changes to the source files.
+
 Having readthedocs.org build the documentation
 ----------------------------------------------