Confusing wording in Add user UI

Problem/Motivation

Confusing wording in "Add user" UI. I'm wasn't sure what this is supposed to mean "This is the text a user may send to the group administrators."

Turns out, this "request message" appears in the Group user admin screen. This is more like "A note about this user's membership".

Original issue is against OG but not prioritized. #1121364: Request message help text

Proposed resolution

Change this text. I cannot make a recommendation, since I don't actually know what its purpose actually is. What was the initial need for it??

Remaining tasks

Figure out what it means, make a patch, test it.

User interface changes

Better text in UI.