Add Makefile for entity relational diagrams, organize docs

[hancush]

Overview

This PR adds a Makefile for diagrams of our core models (person, organization, violation), plus locations, which shows areas of operation and emplacements for organizations, to keep the organization diagram reasonable in size. The output of this recipe is stored in docs/diagrams/.

It also moves docs from the root directory to a new docs/ directory.

Testing Instructions

• Rebuild the app image.
• Delete and rebuild the diagrams:

docker-compose run --rm app make clean_diagrams
docker-compose run --rm app make diagrams