Fill out `src/README.md`

[ReedClanton]

Description

Remove TODOs from the src/README.md, expand what's there, and add any missing sections. However, the environment setup script should probably be in a better state before this is done, so this is blocked by #47.

High Level Solution Description

None.

Alternative Solution(s)

None.

Blocked By

• Environment Setup Script Clean Up #47

Blocking

• None

Related Issue(s)

• None

Additional Context

None.