Added CONTRIBUTING.rst file

Change-Id: I7edb273d36ba3536d5538029377e7b7535cfd115

Author: venkatamahesh

CONTRIBUTING.rst

@@ -0,0 +1,16 @@
+If you would like to contribute to the development of OpenStack,
+you must follow the steps documented at:
+
+   http://docs.openstack.org/infra/manual/developers.html#development-workflow
+
+Once those steps have been completed, changes to OpenStack
+should be submitted for review via the Gerrit tool, following
+the workflow documented at:
+
+   http://docs.openstack.org/infra/manual/developers.html#development-workflow
+
+Pull requests submitted through GitHub will be ignored.
+
+Bugs should be filed on Launchpad, not GitHub:
+
+   https://bugs.launchpad.net/python-openstackclient