Add CONTRIBUTING.rst

There is no CONTRIBUTING.rst file, the patch will add it.

Change-Id: I6e0638a7d2cfb71ab7d830de4a431279f369fc51

Author: liuqing

CONTRIBUTING.rst

@@ -0,0 +1,18 @@
+If you would like to contribute to the development of OpenStack,
+you must follow the steps documented at:
+
+   http://docs.openstack.org/developer/horizon/contributing.html
+
+   or https://wiki.openstack.org/wiki/How_To_Contribute#If_you.27re_a_developer
+
+Once those steps have been completed, changes to OpenStack
+should be submitted for review via the Gerrit tool, following
+the workflow documented at:
+
+   https://wiki.openstack.org/GerritWorkflow
+
+Pull requests submitted through GitHub will be ignored.
+
+Bugs should be filed on Launchpad, not GitHub:
+
+   https://bugs.launchpad.net/horizon