Fix a typo on Almanac User Guide

Summary:
Ref T10527
The lack of a * messed up the remarkup.

Test Plan:
Tested on my instance by pasting the sentence in a phriction document.
See the markup correctly done.

Reviewers: epriestley, Blessed Reviewers

Reviewed By: epriestley, Blessed Reviewers

Subscribers: Korvin

Maniphest Tasks: T10527

Differential Revision: https://secure.phabricator.com/D15421