Highlight code

If `<code>...</code>` is highlighted, this guides will be more user-friendly.

Before:
![ 2013-03-22 3 21 37](https://f.cloud.github.com/assets/290782/287337/27328370-9255-11e2-8af4-89b646220de0.png)

After:
![ 2013-03-22 3 22 28](https://f.cloud.github.com/assets/290782/287338/29ee6b92-9255-11e2-95f1-805b3574bbeb.png)