Document wiki relative link syntax

Summary: Also make ../ work to start relative a link so I don't have to document it as ./../path.

Test Plan:

• Used ./, ../. ./../, and normal links (proper title pickup).
• Used bad links (red).
• Regenerated documentation:

{F1221692}

Reviewers: hach-que

Reviewed By: hach-que

Differential Revision: https://secure.phabricator.com/D15734