Add CONTRIBUTING.rst
Add CONTRIBUTING.rst

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

Change-Id: Ifcdc30b47b5fb668bbca2e974d8cff63a938addb

gotostack/neutron-lbaas,gandelman-a/neutron-lbaas,gandelman-a/neutron-lbaas,citrix-openstack-build/neutron-lbaas,dougwig/x-neutron-lbaas,gotostack/neutron-lbaas,gandelman-a/neutron-lbaas,gotostack/neutron-lbaas