Adds Docker Image v1 Spec Documention

Docker-DCO-1.1-Signed-off-by: Josh Hawn <josh.hawn@docker.com> (github: jlhawn)
This specification is an admittedly imperfect description of an imperfectly-understood problem. Docker is, in turn, an attempt to implement this specification. Our goal and our execution toward it will evolve over time, but our primary concern in this specification and in our implementation is compatibility and interoperability.