corrected styling mistake I had introduced to the 'prerequisites' section of the index.md page

Author: emcaulay

index.md

@@ -19,4 +19,5 @@ root: .
 > ## Prerequisites
 >
 > 1. Setup a [GitHub account](https://github.com/)
-> 2. [Install git on your own computer](https://help.github.com/articles/set-up-git/)
+> 2. [Install git on your own computer](https://help.github.com/articles/set-up-git/) 
+{: .prereq}