update help:upload notice

help:upload notice says fully ai-generated posts are banned

I would imagine this is still true (lol), but there are probably higher priority things to put on the upload notice

This is just imported from Danbooru, but it still applies, and we don't want people uploading slop. It has to be a short notice, but if you have ideas on what else to put there please share them.

Paid reward and rating:e ban are probably more priority things to list to random users unless there's a deluge of fake AI cosplay I'm not aware of

It's not meant to be a duplicate of help:upload rules (though the AI ban might also belong there)