Implement MathJax

If a post needs to render math equations, it only has
to include the mathjax.json params.

content/blog/2019-07-01-Mainline-Hero.md

@@ -1,3 +1,4 @@
+<!-- params: mathjax.json -->
 <!-- title: Mainline Hero Part 0 - Modern Linux For My Galaxy S7 -->
 
 Ever heard of [PostmarketOS](https://postmarketos.org/)? If not, then here's a short summary: