Modernize Arcanist documentation

Summary: Change project_id to project.name and conduit_uri to phabricator.uri.

Test Plan: grep

Reviewers: #blessed_reviewers, epriestley

Reviewed By: #blessed_reviewers, epriestley

Subscribers: epriestley, Korvin

Differential Revision: https://secure.phabricator.com/D9736