I've got a Google Photos album which I've shared with other users via the Get shareable link feature. I'd like them to be able to add photos to this album. How do I do that?
P.S. I've googled for an answer, but find the various apparently out-of-date documentation for Google Photos, Google Plus, Google Picasa very confusing and not applicable. I'm hoping someone who understands it all better than me can give me a straight answer!