CodeLab documentation

I’ve created some work-in-progress documentation for CodeLab. This covers the actual features of CodeLab; nothing code related. It is written in markdown files, and then MkDocs is used to build those files into a website.

https://toehead2001.github.io/codelab-docs/

Each page has an edit icon in the top right corner. Feel free to fill in any missing content. A GitHub account to required to submit changes though.