Adds Docker Image v1 Spec Documention

Docker-DCO-1.1-Signed-off-by: Josh Hawn <josh.hawn@docker.com> (github: jlhawn)
What is a "filesystem change"? Clearly it has "execution parameters", so a change is something executable? In the next sentence they're "change sets"?

What does it mean to "run" a Docker container? Are all containers "runnable"? You claim all ancestors of a Docker container are runnable, but some may not include the "CMD" or "ENTRYPOINT" commands added in later layers.

I'm worried that the goal of this effort -- adding a rigorous specification that enables independent implementations -- is at risk if we start off already assuming tons of context about how the official Docker client works in December 2014.