Document beam-migrate tool

I would love to be able to help with this as right now I am fighting through trying to figure out how to use the beam-migrate tool and package. I understand not all features are yet implemented but I had the following questions and would like to figure out how to PR some documentation in as I can get them solved.

I can currently articulate the following questions?
1. What is the `MODULE` component of the command that it is expecting during a `beam-migrate database add _`?
2. What is a valid format for the connection string? We could go with either an example or a standard if there is one.
3. Is there a way to write the DDL ourselves in Haskell, if so, is there any example code or usage that would indicate how this would work?