bug#9174: give help-gnu-emacs listinfo page URL

[Drew Adams]

> > On (info "(emacs) Service") mention
> > https://lists.gnu.org/mailman/listinfo/help-gnu-emacs
> > so people can see the archives before posting.
> 
> Including URLs in the manuals always means more work, since these
> invariably change.  So I don't think this is a good idea.

With that logic we should just delete the whole manual, nay, all of the manuals.
That would certainly save work.

Of course such a link should be provided.  That's a no-brainer.  This link
target describes the help mailing list.  That is likely to save work in the end.
And even if it means more support work, it should be done because it helps
users.

What's more, GNU should, if it does not already, have a way to use permanent
links (aka universal linking), so that even if a background URL changes the URL
in the doc can stay the same.  IOW, this is an opportunity to improve how we
link, not just an opportunity to save work or close bugs.

Until such permanent linking is available, please add a normal, "invariably
changing" URL.  Users go to the "work" of reporting such bugs.  The least we can
do is honor that work with a dignified response, and not just reject suggestions
out of hand with the sole argument that they mean a little work.