Rewrite of the main README.

Have done a rewrite. Removed what was essentially my original specification with more of a functional/conceptual description. Am also working on a simple worked example that shows off the CLI (stay tuned for another PR).
This feels a little out of place with all this general ivory information. I'm assuming we might have more "developer docs"  in a separate file, which is where I imagine this might go. Not sure though.