The wiki for Serious Sam speedruns.
At its most basic, you can simply edit files through GitHub's online editor. Make sure to check the preview before submitting a pull request.
For larger changes you may want to build the site locally first. Install mkdocs and the windmill theme.
pip install mkdocs mkdocs-windmill
You can then run mkdocs serve to launch a local, auto-updating, server.
Note that if you're using Python 3.8 you will run into mkdocs issue #1885. To fix it manually replace your serve.py with the updated version in the repo.