Gitea (and presumably GitHub) Markdown
This cheatsheet is what works (and in a few cases, doesn't work) in Gitea. I'm presuming that this will also work on GitHub but I would need to post it there before I can confirm.
The pdf version is courtesy of Pandoc. Converting markdown files to pdf is as easy as the following command:
pandoc markdown.md -o markdown.pdf
Very useful, indeed!