bug#28777: Clarifying the temporary documentation update marks in etc/NEWS

[Eli Zaretskii]

> From: Phil Sainty <psainty@orcon.net.nz>
> Cc: Eli Zaretskii <eliz@gnu.org>
> Date: Tue, 10 Oct 2017 23:16:16 +1300
> 
> etc/NEWS says:
> 
> > +++ indicates that all necessary documentation updates are complete.
> >     (This means all relevant manuals in doc/ AND lisp doc-strings.)
> > --- means no change in the manuals is needed.
> 
> If I now understand correctly, "---" means that all relevant lisp doc
> strings have been updated, and "+++" means the same thing and that
> there have additionally been updates to the manual?
> 
> If so, then I think this text could be clarified:

Thanks, I've clarified it.