Diviner: Clarify how to configure Auth providers as an admin
Summary:
* Use a consistent style to cover accessing applications. See D26353.
* Be explicit about accessing the Auth application in the web UI as `./bin/auth` on the command line also exists. See https://superuser.com/questions/1869389/how-to-add-authentication-providers-in-phorge-phabricator
Test Plan:
* Run `./bin/diviner generate`
* Look at the navigation items in http://phorge.localhost/book/phorge/article/configuring_accounts_and_registration/#overview
Reviewers: O1 Blessed Committers, mainframe98
Reviewed By: O1 Blessed Committers, mainframe98
Subscribers: mainframe98, tobiaswiese, valerio.bozzolan, Matthew, Cigaryno
Differential Revision: https://we.phorge.it/D26354