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.
Originally borrowed from [Joshua Pekera's excellent template](https://gist.github.com/joshuapekera/5730539/), and since much amended. For more complete info, see [John Gruber's original spec](http://daringfireball.net/projects/markdown/) and the [Github-flavored Markdown info page](http://github.github.com/github-flavored-markdown/).