Change release note link to OpenStack docs site

1. What is the problem
Currently release note link in readme is linked to github site,
should be updated to OpenStack docs site.

2. What is the solution to the problem
Link release note to OpenStack docs site

3. What the features need to be implemented to the Tricircle
No new features

Change-Id: I1b7798ec101a917e1297f02c8e71c6001264b6df

README.rst

@@ -53,5 +53,5 @@ detailed in the LICENSE file.
 * Source: http://git.openstack.org/cgit/openstack/tricircle
 * Bugs: http://bugs.launchpad.net/tricircle
 * Blueprints: https://blueprints.launchpad.net/tricircle
-* Release notes: https://github.com/openstack/tricircle/tree/master/releasenotes/notes
+* Release notes: http://docs.openstack.org/releasenotes/tricircle
 * Contributing: http://docs.openstack.org/developer/tricircle/contributing.html