document that binary images are now deprecated

Support for binary images gets removed in Z cycle.

Change-Id: I9cd93a2022d6b9d17f326d55d57f86cb5e141e7d

Author: hrw

doc/source/admin/image-building.rst

@@ -124,6 +124,11 @@ installed from upstream sources. The default method of the OpenStack install is
 
    kolla-build -t binary
 
+.. note::
+
+   Building of binary images is deprecated in Yoga. Please switch to source
+   ones.
+
 The locations of OpenStack source code are written in ``kolla-build.conf``.
 The source type supports ``url``, ``git``, and ``local``. The location of
 the ``local`` source type can point to either a directory containing the source

releasenotes/notes/yoga-prelude-4773bac540443b41.yaml

@@ -0,0 +1,5 @@
+---
+prelude: |
+    Binary images are deprecated in Yoga and any support for them will be
+    removed in the next cycle. Users are requested to migrate to source based
+    images.