In Monitoring User Guide, link to Flower docs

Addresses issue #2292

docs/userguide/monitoring.rst

@@ -255,6 +255,11 @@ Then, you can visit flower in your web browser :
 
     $ open http://localhost:5555
 
+Flower has many more features than are detailed here, including
+authorization options. Check out the `official documentation`_ for more
+information.
+
+.. _official documentation: http://flower.readthedocs.org/en/latest/
 
 
 .. _monitoring-celeryev: