Further api-quick-start edits

Update app-support file with move of api-quick-start,
add releasenote for the move.

Change-Id: Iaa7a75091170436d1b953583f602514e43f41b0e

doc/common/app-support.rst

@@ -50,7 +50,7 @@ The following book explains how to use the command-line clients:
 The following documentation provides reference and guidance information
 for the OpenStack APIs:
 
-*  `API Documentation <https://developer.openstack.org/api-guide/quick-start/>`_
+*  `API Documentation <https://docs.openstack.org/api-quick-start/>`_
 
 The following guide provides information on how to contribute to OpenStack
 documentation:

releasenotes/source/index.rst

@@ -20,6 +20,7 @@ Contents
 .. toctree::
    :maxdepth: 2
 
+   train.rst
    rocky.rst
    queens.rst
    pike.rst

releasenotes/source/train.rst

@@ -0,0 +1,7 @@
+=============
+Train release
+=============
+
+* The API Guide document has been migrated into the
+  ``openstack-manuals`` repository and is published to
+  `docs.openstack.org <https://docs.openstack.org/api-quick-start>`__.