Fill out the minimum information for the README

[christophertubbs]

The README is currently just the one from the template.

Someone needs to fill in the minimum amount of information, giving details on what to expect from the repo, the knowledge that we have right now, and stubs for information that will come later (such as the table from #2 and the diagrams from #3).

This would not and should not present a final draft of what the README should look like - just a replacement for the template information and enough breadcrumbs to drive progress if this repository goes dormant for one reason or another.