Adds Docker Image v1 Spec Documention

Docker-DCO-1.1-Signed-off-by: Josh Hawn <josh.hawn@docker.com> (github: jlhawn)
I would phrase it something like this:

Images are composed of "layers".  An image layer is a general term which may be used to refer to one or both of the following:

1. The JSON metadata for a layer _(ed: which defines what exactly?)_
2. The filesystem changes described by a layer

To refer to the former specifically, the terms "Layer JSON" or "Layer Metadata" are frequently used.

To refer to the latter, the terms "Image Filesystem Changeset" or "Image Diff" are frequently used.



WDYT?