doc: add a release notes page for west

This just documents what's already happened.

A subsequent patch will extend it for v0.6.x.

Signed-off-by: Marti Bolivar <marti.bolivar@nordicsemi.no>

doc/guides/west/index.rst

@@ -44,6 +44,7 @@ context about the tool.
    why.rst
    without-west.rst
    planned.rst
+   release-notes.rst
 
 For details on west's Python APIs (including APIs provided by extensions in the
 zephyr), see :ref:`west-apis`.

doc/guides/west/release-notes.rst

@@ -0,0 +1,25 @@
+West Release Notes
+##################
+
+v0.5.x
+******
+
+West v0.5.x is the first version used widely by the Zephyr Project as part of
+its v1.14 Long-Term Support (LTS) release. The `west v0.5.x documentation`_ is
+available as part of the Zephyr's v1.14 documentation.
+
+West's main features in v0.5.x are:
+
+- Multiple repository management using Git repositories, including self-update
+  of west itself
+- Hierarchical configuration files
+- Extension commands
+
+Versions Before v0.5.x
+**********************
+
+Tags in the west repository before v0.5.x are prototypes which are of
+historical interest only.
+
+.. _west v0.5.x documentation:
+   https://docs.zephyrproject.org/1.14.0/guides/west/index.html