RO-958 Add guidelines for backporting
RO-958 Add guidelines for backporting

This patch adds instructions for the lovely process of backporting
patches into older branches.

cloudnull/rpc-openstack,rcbops/rpc-openstack,jacobwagner/rpc-openstack,rcbops/rpc-openstack,git-harry/rpc-openstack,mancdaz/rpc-openstack,jacobwagner/rpc-openstack,hughsaunders/rpc-openstack,robb-romans/rpc-openstack,prometheanfire/rpc-openstack,hughsaunders/rpc-openstack,BjoernT/rpc-openstack,git-harry/rpc-openstack,prometheanfire/rpc-openstack,BjoernT/rpc-openstack,mancdaz/rpc-openstack,robb-romans/rpc-openstack,cloudnull/rpc-openstack