Adds remaining Debian notes

This patch adds Debian specific comments for the installation
of Ceilometer, Heat and neutron.

backport: havana

Change-Id: Iff88e1919dce2e3b6e8fb78e79a53d3b5c898c96
(cherry picked from commit 18083a02fa40fa665e0da1f0269bd4b847553364)