migration-3.4: add some extra packaging notes

Add some notes on minor packaging changes that I missed earlier.

(From yocto-docs rev: a4f345f888b466bd1459b767c1b8cf8b9397e27e)

Signed-off-by: Paul Eggleton <paul.eggleton@microsoft.com>
Reviewed-by: Michael Opdenacker <michael.opdenacker@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

documentation/migration-guides/migration-3.4.rst

@@ -202,6 +202,15 @@ Package/recipe splitting
   in its own ``xwayland`` recipe. If you need Xwayland in your image
   then you may now need to add it explicitly.
 
+- The ``rpm`` package no longer has ``rpm-build`` in its :term:`RRECOMMENDS`;
+  if by chance  you still need rpm package building functionality in
+  your image and you have not already done so then you should add
+  ``rpm-build`` to your image explicitly.
+
+- The Python ``statistics`` standard module is now packaged in its own
+  ``python3-statistics`` package instead of ``python3-misc`` as
+  previously.
+
 
 Image / SDK generation changes
 ------------------------------