Add release notes job to zuul template

We are not running the release notes job, so are unable to
see the built release notes when they are included in a patch.
Add it as in the other neutron repos.

Also added a similar README.rst as the neutron repo to give
the basic info on release note generation, and fixed up
various issues in the configuration description.

Change-Id: I98ffed3ed77a16bba59cae69a73cb699ddb175fb
diff --git a/README.rst b/README.rst
index b3883b8..3d8a49b 100644
--- a/README.rst
+++ b/README.rst
@@ -10,3 +10,4 @@
 * Documentation: https://docs.openstack.org/neutron/latest/
 * Source: https://git.openstack.org/cgit/openstack/neutron-tempest-plugin
 * Bugs: https://bugs.launchpad.net/neutron
+* Release notes: https://docs.openstack.org/releasenotes/neutron-tempest-plugin/