Rewrite README.md and move current content to CONTRIBUTING.md

[thundergolfer]

A lot of the content in the README.md is intended for contributors to the project, where it is actually typical of the README.md to be something to promote and explain the project to outsiders.

So really a new CONTRIBUTING.md should be created and the content relevant to that in the README.md should be moved in.

The README.md can be left a bit empty after this, but maybe add the skeleton with sections to eventually fill. Key sections would be a section with demonstration images, a features section, and a section explaining how others can 'spin up' our project on their own machine.