Implemented documentation for XML-feed. Still need to add the validation form (and possibly the signup form).

Summary: Arcanist is behaving weird. You'll probably get too many revisions.

Test Plan: Browse through the pages

Reviewers: claassen, #uitzendbureau.nl

Reviewed By: claassen, #uitzendbureau.nl

Differential Revision: http://phabricator.uzbdev.nl/D322