add ceilometer to gnocchi configuration notes
add ceilometer to gnocchi configuration notes

first notes on how to enable ceilometer to connect to gnocchi

Change-Id: I13840eb0ff0a74534fec6b5b52e011fd7fc20a8b

openstack/ceilometer,ityaptin/ceilometer,openstack/ceilometer,ityaptin/ceilometer