Adds Docker Image v1 Spec Documention

Docker-DCO-1.1-Signed-off-by: Josh Hawn <josh.hawn@docker.com> (github: jlhawn)
Well, what are you trying to communicate here? Or, more specifically, what's the important new info you are trying to convey to the reader? That the spec is constantly evolving? That Docker is an implementation of this spec? That Docker is constantly evolving? Some or all of those? None of those? Tell me, and I'll show you how to revise so that it gets across.