doc: getting_started: run west update after pulling zephyr

This is causing confusion.

Signed-off-by: Marti Bolivar <[email protected]>

Author: mbolivar-nordic

doc/getting_started/index.rst

@@ -96,6 +96,16 @@ Clone all of Zephyr's repositories in a new :file:`zephyrproject` directory:
 You can replace :file:`zephyrproject` with another directory name. West creates
 the directory if it doesn't exist. See :ref:`west-multi-repo` for more details.
 
+.. important::
+
+   You need to run ``west update`` any time :file:`zephyr/west.yml` changes.
+   This command keeps :ref:`modules` in the :file:`zephyrproject` folder in sync
+   with the code in the zephyr repository, so they work correctly together.
+
+   Some examples when ``west update`` is needed are: whenever you
+   pull the :file:`zephyr` repository, switch branches in it, or perform a ``git
+   bisect`` inside of it.
+
 .. warning::
 
    Don't clone into a directory with spaces anywhere in the path.