Revise README; coordinate with project wiki

[JimHafner]

Coordinate README with project wiki (issue #32).

[JimHafner]

As part of this, I am also taking on issue #119

[morisy]

Thanks for taking this on Jim!

Some good examples to steal from:

• https://github.com/codeforboston/clean-slate/wiki
• https://github.com/codeforboston/clean-slate
• https://github.com/codeforboston/voiceapp311
• https://github.com/codeforboston/voiceapp311/wiki
  ReadMe should be greatly shortened with most of it moved to Wiki, but the ReadMe should give people a quick understanding of what the project is about and links to dig in deeper.

[JimHafner]

3/10/2020
Have put in pull request for rewrite of README. As part of this, I have moved installation instructions and code formatting info to new wiki pages.