bug#50674: Major mode for etc/AUTHORS with basic font-locking

[Eli Zaretskii]

> From: Stefan Kangas <stefan@marxist.se>
> Date: Tue, 21 Sep 2021 01:58:58 -0700
> Cc: juri@linkov.net, 50674@debbugs.gnu.org
> 
> Eli Zaretskii <eliz@gnu.org> writes:
> 
> > You mean, binary distributions?  Do we care?  Do users of binary
> > distributions read the AUTHORS file?
> 
> It is reachable from the splash screen, so yes.

The splash screen button could load the file from any place we want,
so if that is the problem, I don't understand all the sub-thread about
where to put the file.  E.g., we could put it in etc/.