Create markdown documentation for database schemas

[jts599]

Is your feature request related to a problem? Please describe.
Currently, the database schemas are only documented in code.

Describe the solution you'd like
Create a markdown page with a more human readable representation of the database structure

Describe alternatives you've considered
There are other more human readable formats that could be used, but Github markdown seems to be a natural fit.

Additional context
I have a script that generates an (admittedly basic) markdown page for the schemas in my fork's transform/src/schemas directory.