Add release notes link in README
Add release notes link in README

Change-Id: I3eee7c2cd46e5386b17df22c023bde037ebac627

openstack/networking-bagpipe-l2,stackforge/networking-bagpipe-l2,stackforge/networking-bagpipe-l2,openstack/networking-bagpipe,openstack/networking-bagpipe-l2,openstack/networking-bagpipe