Document GET and POST reports endpoints

[ap2322]

Add documentation for the GET and POST /api/v1/reports endpoints in the README

This is based on my understanding of the code and issues surrounding making reports.

TODOs realized while writing this (already created issues for these on the project board):

• We need to make sure our POST /api/v1/reports endpoint does not create duplicate locations
• We need to add authentication to our api with a query param service_key=[SERVICE_KEY]
• Fix a seed error by adding a dependent destroy to locations

@Dustin-Mikusko, feel free to make edits directly to the README before merging

Closes #27