Add container spec

This document specifies the current container specification with all the
underlying setup and configuration that goes into making a container.
This is the v1 spec that is today but allows for flexability when we
introduce more features such as seccomp default profiles and more.

Signed-off-by: Michael Crosby <crosbymichael@gmail.com>
Do we assume that mount namespace is always available and enabled? If its not, we might have to fall back to chroot.