Adding cue to plugin registry

Adding cue to the plugin registry under "Official OpenStack Projects"

Change-Id: I24fc76eb6aadb653c0db5a0fa1d8e22cd166dbe9
diff --git a/doc/source/plugin-registry.rst b/doc/source/plugin-registry.rst
index c68d926..0740ba0 100644
--- a/doc/source/plugin-registry.rst
+++ b/doc/source/plugin-registry.rst
@@ -28,6 +28,8 @@
 +------------------+---------------------------------------------+--------------------+
 |congress          |git://git.openstack.org/openstack/congress   | governance         |
 +------------------+---------------------------------------------+--------------------+
+|cue               |git://git.openstack.org/openstack/cue        | message-broker     |
++------------------+---------------------------------------------+--------------------+
 |gnocchi           |git://git.openstack.org/openstack/gnocchi    | metric             |
 +------------------+---------------------------------------------+--------------------+
 |magnum            |git://git.openstack.org/openstack/magnum     |                    |