[New] Add Guidance for Studio Codes

[AdultSun]

We need to add new sections providing guidance on the studio codes field. Unofficial/unapproved should be fine at first for this, there seems to be a pretty solid consensus for how we've been using it already.

This will likely need to include specific examples for how we handle network/studio X, Y, and Z. We've gotten a few questions on Discord already about that, "Where do I find the studio code for this particular site? Is it the number in the URL or something else?"