[docs] Use slightly more proper .rst markup

[docs] Use slightly more proper .rst markup

Again, I'd like to emphasize to everyone that this sort of markup change
is *not* what you should be concerned about when writing docs. Focus on
*content*.

I applaud Chandler for focusing on the fantastic content of this new
section!

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@227305 91177308-0d34-0410-b5e6-96231b3b80d8