R1:6d5920fa2d23

Improve help for "bin/policy unlock" to make it explicit that you can name objects with a PHID

Summary: See <https://discourse.phabricator-community.org/t/how-to-unlock-a-portal-to-view-edit-it-as-an-admin-similar-to-tasks/4547/>.

Test Plan: Ran `bin/policy help unlock`, saw explicit "you can use a PHID" documentation.

Differential Revision: https://secure.phabricator.com/D21530