Displays the part names in the header

<img width="379" alt="screen shot 2016-07-22 at 12 48 47" src="https://cloud.githubusercontent.com/assets/5644953/17055049/a9509f10-500a-11e6-9a3c-ff22dbb6bf6c.png">

Example from help.gitbook.com

This FAQ entry should be listed in `FAQ / Basic / What is GitBook ?`
