Good documentation should be readable from source, and usable to generate fancy HTML. That's why RST is so commonly used:
readable as text source, usable to generate HTML and even PDF GitHub knows how to render it, Sphinx and ReadTheDocs know how to render it. Good documentation should often show code. This article demonstrates an inconsistency between RTFD and GitHub rendering, and how to fix it.
As far as sphinx is concerned, the default highlight language for code blocks is Python.