I just noticed a unobtrusive little link below the right lower corner of a photos comment box, offering "Suggest a group..."
Bravely I clicked the link, and a box opened, telling me:
Here is a new way of inviting to add a doc to your groups:
Anyone noticed that already?
And another thing I just noticed when saving this post as draft: The link also apears here under the comment box... a little bug? ;-)