Add releasenotes link to README

Change-Id: I8fae29dd0656530c3331a70866cff554ad5e495b

README.rst

@@ -9,5 +9,6 @@ based on `Ironic Python Agent`_.
 * Documentation: https://docs.openstack.org/ironic-python-agent-builder
 * Source: https://opendev.org/openstack/ironic-python-agent-builder
 * Bugs: https://storyboard.openstack.org/#!/project/948
+* Release Notes: https://docs.openstack.org/releasenotes/ironic-python-agent-builder/
 
 .. _Ironic Python Agent: https://docs.openstack.org/ironic-python-agent