Adds MathJax support to GitHub Gists. Useful for working with Markdown documents.

mathjax-gist.user.js

// ==UserScript==
// @name       MathJax for Gists
// @include    *://gist.github.com/*
// @version    0.1
// @description  Adds MathJax support to Gists.
// ==/UserScript==

if ((window.unsafeWindow == null ? window : unsafeWindow).MathJax == null) {
    var script = document.createElement("script");
    script.type = "text/javascript";
    script.src = "https://c328740.ssl.cf1.rackcdn.com/mathjax/latest/MathJax.js?config=TeX-AMS-MML_HTMLorMML";
    document.getElementsByTagName("head")[0].appendChild(script);
}

How do I use this? I have a markdown file with math. Where should I put this file?

If this does what it says, it would be incredibly useful... If I knew how to use it

seem to be a userscript. you need grease monkey or equivalent plugin to run it :)