Document overall system structure

[dsummersl]

It'd be great to have some overview of the tech stack as it stands. Obvious things that would be nice to have the main README.md file:

• That angular works directly with firebase.
• That express mainly serves static content.
• The angular app uses Leaflet, and bootstrap.
• Where the main controllers are.
• There are test cases! Just point them out.

[dsummersl]

https://brigades.opendatanetwork.com/TRANSPORTATION/North-Carolina-Bicycle-Crash-Data/5tve-iede