[Update] Approve "Merging Sorted Tags"

[AdultSun]

Needs official approval:
https://guidelines.stashdb.org/docs/tags/merging-tags/#merging-sorted-tags

This is another rule of thumb I came up with on my own back in the Google Doc days for the guidelines. Essentially, it's an extension of my definition of "sorted" tags explained in the Getting Started page.

I could probably soften the language of this section, but the point is that tag merges should be more closely examined if it removes a tag that's already been defined by another contributor. This likely means that a determination was previously made that it should remain separate from other existing tags and that this decision shouldn't be overruled without serious consideration.