Add a release note link on README

Release notes are managed on reno mechanism and the contents are
generated automatically on a link. So this patch adds the link for
users who are interested in Tempest versioning.

Change-Id: Ieef7310e1571a0a13832203670c61b5f77f0c3f3
diff --git a/README.rst b/README.rst
index 13f4f61..3c0463b 100644
--- a/README.rst
+++ b/README.rst
@@ -124,6 +124,9 @@
 
 Release Versioning
 ------------------
+`Tempest Release Notes <http://docs.openstack.org/releasenotes/tempest>`_
+shows what changes have been released on each version.
+
 Tempest's released versions are broken into 2 sets of information. Depending on
 how you intend to consume tempest you might need