Initial Dockerfile

[nickv2002]

This adds a dockerfile that can be built more easily and platform-agnostic than the Python virtual env and some instructions for how to run that via CLI. This was based on my own suggested in another PR.

@sumpfork LMK if you have questions, otherwise go ahead and merge this.

Potential next steps:

1. Build the dockerfile via GitHub Workflows and host a pre-built one in this project
2. Add additional dockerfile-based testing steps to make testing easier
3. Add instructions to bind mount the project dir to use docker in development iteration loop

[sumpfork]

This is fine to add, too, but I was thinking of something much simpler to start: #502.