bug#50880: Add "Contributing to Emacs" help command (see C-h C-h)

[Stefan Kangas]

Gregory Heytings <gregory@heytings.org> writes:

> What was wrong with
>
> C-h g -> About the GNU project
> C-h G -> Emacs copying permission (GNU General Public License)
> C-h C-c -> Contributing

IMO the best proposal so far, but Lars didn't want to move the GPL
from 'C-h C-c' so that part unfortunately makes it a non-starter.

> Also, I would put "Contributing to Emacs" in the first subsection of
> "Miscellaneous", after "Debugging Emacs", where it belongs.  Which by the
> way makes me wonder why Emacs TODO is not there, too.  It would perhaps be
> even better to create a third subsection with
>
> C-p Known problems
> C-d Debugging Emacs
> ?   Contributing to Emacs
> C-t Emacs TODO

Good idea, I like it.