I'd like to be able to include MathJax for LaTeX formatting in all questions and answers on my site. According to the MathJax site:
To use MathJax from our server, you need to do two things:

Link MathJax into the web pages that are to include mathematics.

Put mathematics into your web pages so that MathJax can display it.
You accomplish the first step by putting
<script type="text/javascript"
src="http://cdn.mathjax.org/mathjax/latest/MathJax.js?config=TeXAMSMML_HTMLorMML">
</script>
into the <head>
block of your document.
Which document should I paste this code into?