Document how to install custom wheels

[virtuald]

I believe you can do python -m robotpy installer install /path/to/foo.whl, just make sure to remove it from your pyproject.toml (or pin it to your version) otherwise the deploy might decide to install the other version.

https://www.chiefdelphi.com/t/using-forked-libraries-with-robotpy/497776/2

Probably should document this and add something to make it so that the deploy doesn't overwrite the manually installed version.