Add supervisor_cgroups to the plugins list

docs/plugins.rst

@@ -81,6 +81,10 @@ These also includes various event listeners.
 `supervisor-logging <https://github.com/infoxchange/supervisor-logging>`_
     An event listener that sends process log events to an external
     Syslog instance (e.g. Logstash).
+`supervisor_cgroups <https://github.com/htch/supervisor_cgroups>`_
+    An event listener that enables tying Supervisor processes to a cgroup
+    hierarchy.  It is intended to be used as a replacement for 
+    `cgrules.conf <http://linux.die.net/man/5/cgrules.conf>`_.
 
 Libraries that integrate Third Party Applications with Supervisor
 -----------------------------------------------------------------
@@ -146,4 +150,4 @@ with third party applications:
 `dokku-logging-supervisord <https://github.com/sehrope/dokku-logging-supervisord>`_
     `Dokku <https://github.com/progrium/dokku>`_ plugin that injects ``supervisord`` to run
     applications.  It also redirects ``stdout`` and ``stderr`` from processes to log files
-    (rather than the Docker default per-container JSON files).
+    (rather than the Docker default per-container JSON files).