"Add description" confuses users

People are adding edit summaries in the place for message documentation, perhaps because there's no other place where they can explain something (bugzilla:45831?) or perhaps because the button is confusing.

Example: [1], but I've seen several others. I bet this is now the vast majority of qqq edits on Meta, but I can't see it easily because we have no CleanChanges there.

There are too many ways to see this problem, I'm unable to translate it to a bugzilla report; I've mentioned it on bugzilla:45831#c5. It's also possible that we must get used to a new role of message documentation, it could get interesting.

Slight reword in gerrit:61761.