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

[Eli Zaretskii]

> From: Lars Ingebrigtsen <larsi@gnus.org>
> Cc: stefan@marxist.se,  gregory@heytings.org,  50880@debbugs.gnu.org
> Date: Fri, 01 Oct 2021 12:20:55 +0200
> 
> Eli Zaretskii <eliz@gnu.org> writes:
> 
> >> Me too.
> >
> > Which part?  If this is about the manual organization, I fail to see
> > what's wrong with the current one, where Contributing is a chapter --
> > you don't get any more prominent than that.
> 
> No, this is the `C-h C-h' buffer output.

But then all of those are already there?