Add plug-in summary for osc doc
Add plug-in summary for osc doc

Stevedore Sphinx extension handles this comment.
http://docs.openstack.org/developer/python-openstackclient/plugin-commands.html

Change-Id: I06db0b2c04e5e4bb395b68c1640bec7c6588895b

stackforge/python-senlinclient,openstack/python-senlinclient,stackforge/python-senlinclient,openstack/python-senlinclient