R1:20fb93d1a4be

Add small documentation details

Summary:
Add some small Diviner documentation details like:

* mention PHP 8.1 (thanks https://we.phorge.it/Q18)
* mention the fact that you need multiple databases (it may be not obvious from the startup)
* mention MariaDB and not just MySQL (thanks MariaDB community!)
* mention "Administrator" and not just "User" for the "Instructions for installing, configuring, and using Phorge."

I was not bold enough to do more changes.

Test Plan: I tested locally and Diviner does…