migration-guides: Add coverage of addpylib directive

To complement what I am adding to the BitBake reference manual, add a
section in the 4.2 migration guide, a reference in the structure section
of the reference manual (where we talk about meta/lib) and adjust the
release notes item to be a little more concise.

(From yocto-docs rev: 0903e82a9da263c6d64aead03407eb377eb5bbfe)

Signed-off-by: Paul Eggleton <bluelightning@bluelightning.org>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

documentation/migration-guides/migration-4.2.rst

@@ -85,6 +85,28 @@ On the other hand, some earlier distributions are no longer supported:
 
 See :ref:`all supported distributions <system-requirements-supported-distros>`.
 
+
+.. _migration-4.2-addpylib:
+
+Python library code extensions
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+BitBake in this release now supports a new ``addpylib`` directive to enable
+Python libraries within layers.
+
+This directive should be added to your layer configuration
+as in the below example from ``meta/conf/layer.conf``::
+
+   addpylib ${LAYERDIR}/lib oe
+
+Layers currently adding a lib directory to extend Python library code should now
+use this directive as :term:`BBPATH` is not going to be added automatically by
+OE-Core in future. Note that the directives are immediate operations, so it does
+make modules available for use sooner than the current BBPATH-based approach.
+
+For more information, see :ref:`bitbake-user-manual/bitbake-user-manual-metadata:extending python library code`.
+
+
 .. _migration-4.2-misc-changes:
 
 Miscellaneous changes

documentation/migration-guides/release-notes-4.2.rst

@@ -11,12 +11,8 @@ New Features / Enhancements in 4.2
    :term:`buildtools` tarball.
 
 -  BitBake in this release now supports a new ``addpylib`` directive to enable
-   Python libraries within layers.
-
-   This directive should be added to your layer configuration
-   as in the below example from ``meta/conf/layer.conf``::
-
-      addpylib ${LAYERDIR}/lib oe
+   Python libraries within layers. For more information,
+   see :ref:`bitbake-user-manual/bitbake-user-manual-metadata:extending python library code`.
 
 -  BitBake has seen multiple internal changes that may impact
    memory and disk usage as well as parsing time, in particular:

documentation/ref-manual/structure.rst

@@ -750,7 +750,9 @@ and lists of files and directories with known permissions.
 -------------
 
 This directory contains OpenEmbedded Python library code used during the
-build process.
+build process. It is enabled via the ``addpylib`` directive in
+``meta/conf/local.conf``. For more information, see
+:ref:`bitbake-user-manual/bitbake-user-manual-metadata:extending python library code`.
 
 .. _structure-meta-recipes-bsp: