Add Rackspace resources summary to docs
Add Rackspace resources summary to docs

Add information regarding general use case, dependencies, and README
info for Rackspace resources in the contrib docs.

Closes-Bug: #1271226
Change-Id: I3a57cd5f1e72663bd283d96c07949ff6de23df3a

steveb/heat,maestro-hybrid-cloud/heat,redhat-openstack/heat,noironetworks/heat,jasondunsmore/heat,pratikmallya/heat,cwolferh/heat-scratch,ntt-sic/heat,dragorosson/heat,NeCTAR-RC/heat,redhat-openstack/heat,maestro-hybrid-cloud/heat,noironetworks/heat,dims/heat,rh-s/heat,NeCTAR-RC/heat,cwolferh/heat-scratch,gonzolino/heat,rdo-management/heat,dragorosson/heat,pshchelo/heat,cryptickp/heat,cryptickp/heat,openstack/heat,ntt-sic/heat,miguelgrinberg/heat,srznew/heat,miguelgrinberg/heat,steveb/heat,gonzolino/heat,rdo-management/heat,pratikmallya/heat,rh-s/heat,takeshineshiro/heat,srznew/heat,openstack/heat,takeshineshiro/heat,pshchelo/heat,jasondunsmore/heat,dims/heat