Just my two cents:
Ask the people of groups.io if it is possible to have two "sticky" messages always on top of the list so new users and existing users too can read.
First explain the basics of how to use, eg. How to create a new message and a new album using the same name, copy/paste the link to the album in the new message so the relevant images are easy to find when reading the thread.
Second sticky: explain the free usage of this group and the relative small amount per user needed to keep it alive and put a "PayPal donate link" in there?
I prefer PayPal too.