Add info on getting the "device" cgroup in it's own heirarchy

I won't be offended if you ignore this pull request, but since I spent a few hours trying to figure this one out I thought I'd throw it your way.

BTW: This is great!  I'm hoping to build a reproducible test suit ontop of this for [a program](https://github.com/subuser-security/subuser) that uses docker :)
Merge pull request #11 from timthelion/patch-1

Add info on getting the "device" cgroup in it's own heirarchy
Support "docker restart"

Delete the pidfile if docker was not shut down properly.
Merge pull request #12 from miracle2k/patch-1

Support "docker restart"
let the caller of wrapdocker pass options to docker and arguments to the spawned shell
redirect out
Merge branch 'master' of github.com:vgeshel/dind