Add CONTRIBUTING.rst file for blazar
Add CONTRIBUTING.rst file for blazar

Change-Id: I9a0c8d3c6282518cf078dd5601da0bf7df540edd
Story: 2007236
Task: 38515

ChameleonCloud/blazar,stackforge/blazar,ChameleonCloud/blazar,openstack/blazar,openstack/blazar,stackforge/blazar