R1:e7eac67cf388

Fix documentation on deprecated phd repository-launch-readonly

Summary: You need to use -- to separate arguments for phd and the daemon.

Test Plan: Ran with the extra --.

Reviewers: epriestley, vrana

Reviewed By: vrana

CC: aran, Korvin

Differential Revision: https://secure.phabricator.com/D3106