It's in the left pane. Basically you have to host your text document (TXT, PDF etc.) somewhere freely accessible on the web (hints as to where to host are in the help on that page) and write an entry for it. Then staff will decide whether or not it's worthwhile having on the site, also based on the correctness of the submission form.
So basically some documentation as to how it works beside source code would do in my opinion. Of course you can also stick source code in there.