Reason for this suggestion is so mods don't have to constantly Google or refer back to Reddit each time they have a question about what permission does what.

Here is Reddit's page to copy: https://www.reddit.com/r/modhelp/wiki/mod_permissions

Could it be added as a separate page/FAQ on the Wiki?

There are a few minor wording updates to be made since Reddit-vs-SaidIt, like reference to old ModMail or viewing ModLog (which are defaults here). But for the most part, everything on the page is fine as-is, and I'm sure mods here can overlook the few discrepancies until it's properly updated.