Optional KaTeX/MathJax support for repositaries

[SageofPHY6Paths]

There are some plugins like MathJax Plugin for Github which if you install then in every repository anything between$ $ will be rendered. But the problem is a different person cannot read them. So I think an option should be given in the repository settings to enable math for that repo for anyone.

LaTeX support is being asked from 2014. Even if it can't be implemented everywhere at least opt in feature must be given. Gitlab also supports it.