Add a README.md file

[webchick]

What was changed

This PR adds a README.md that contains much of the installation instructions written by @steveandroulakis as well as some additional notes that I hit going through.

This still has outstanding TODOs, and I see that the instructions are under active construction, so this may be "won't fix" but figured I'd try and give a stab to get things rolling.

Why?

• This repo is going to be mentioned during the keynote, and people are gonna be curious. :)
• This puts the docs in a file where we can easily see change revisions, etc.
• The folks actively building the demo need to stay focused on that.
• Writing docs is fun for me. :D

[CLAassistant]

All committers have signed the CLA.

[steveandroulakis]

This is great! Will let @robholland review fully and in light of the fact it's probably a quickly-moving target