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