[kemono] fix default coomer file order

[AngeredBacterium]

I noticed the file order was wrong for coomer posts. For OnlyFans, file is first in a few cases I looked at (I checked both coomer & OnlyFans itself) and for Fansly file seems to always be empty anyway.

I'm pretty sure this change will result in different outputs for every OnlyFans post with more than 1 file, but it'll be more correct with it 😅 (but I understand if this means you don't want the change)

I understand it was intentionally set the way it is for kemono, so I've just changed the default for coomer & added it to the docs. Hope I did it correctly!

[mikf]

Maybe the default order should be changed/reverted for kemono as well?

I believe it was initially set to attachments first as a workaround for kemono's tendency to duplicate files for Patreon posts, but I don't think this is necessary anymore.

Related: #1899 #1991 #3054

[AngeredBacterium]

I just re-read through those issues now and I think the current ordering for kemono solved more than that problem. For example the link in this comment links to a patreon post where file is an image and attachments is [zip, image], and the two images are the actual contents of the zip file as well. So reverting to [file, attachments, inline] would make that post order as image, zip, image, which seems weird.