Update README.rst with lastest usage
Update README.rst with lastest usage

With the Mitaka troveclient release imminent, it makes sense to have
the usage that appears on the pypi page up-to-date.

Change-Id: I05870807e51be669ae61b5526af4325c385c04da

Tesora/tesora-python-troveclient,openstack/python-troveclient,Tesora/tesora-python-troveclient,openstack/python-troveclient