[Update] Approve "Preferred Scene Descriptions"

[AdultSun]

Needs official approval:
https://guidelines.stashdb.org/docs/scenes/scene-descriptions/#preferred-scene-descriptions

Most of this is pretty straightforward and very similar to issue #25 and closely related to issue #33. It boils down to us preferring the original official studio description over modified descriptions. It also says that we'd rather have an empty description field instead of unofficial descriptions or placeholder/boilerplate descriptions.

Just like "Preferred Scene Titles", it also does not mention any exceptions to the guideline, even though the section immediately below lists all of the relevant exceptions. We should probably include something like, "See the next section for possible exceptions."

Also just like scene titles, a new feature allowing for alternate descriptions in Stash-Box could help with some of these issues and points of confusion.