Change monospace text formatting

Summary:
Using ## can cause some formatting issues, for example:

As such, use ` instead.

Test Plan: Generated documentation locally.

Reviewers: Blessed Reviewers, epriestley

Reviewed By: Blessed Reviewers, epriestley

Subscribers: Korvin, epriestley

Differential Revision: https://secure.phabricator.com/D13071