Add mypy setup

[dorchard]

Some information about setting up mypy may be helpful for participants ahead of time. E.g., at the very least:

## Getting setup with mypy

Mypy requires Python 3.8 or later to run. You can install mypy using pip:

    $ python3 -m pip install mypy

Once mypy is installed, run it by using the mypy tool:

    $ mypy program.py

You can find more details on [how to get mypy setup on their website](https://mypy.readthedocs.io/en/stable/getting_started.html)