Adding installation instructions for Debian

Setting up CMS on Debian is a bit more involved than on Ubuntu because the cgroups setup requires more manual work (e.g., see https://lists.debian.org/debian-kernel/2012/01/msg00804.html). The steps described in this commit worked for me on Debian testing. The instructions might be useful for other people trying to set up CMS on Debian.
`s/foobar/cgroup`