Update Diviner documentation to reference Phorge instead of Phabricator for Arcanist.
Test Plan: Generated Diviner documentation on a local install and verified that the changes look good.
Reviewers: O1 Blessed Committers, deadalnix
Reviewed By: O1 Blessed Committers, deadalnix
Subscribers: speck, tobiaswiese
Maniphest Tasks: T15012
Differential Revision: https://we.phorge.it/D25008