bug#42400: 26.3; doc of `kill-emacs' optional ARG

[Eli Zaretskii]

> From: Robert Pluim <rpluim@gmail.com>
> Date: Thu, 16 Jul 2020 19:34:40 +0200
> Cc: 42400@debbugs.gnu.org
> 
> >>>>> On Thu, 16 Jul 2020 08:25:55 -0700 (PDT), Drew Adams 
> >>>>> <drew.adams@oracle.com> said:
> 
>     Drew> Both the Emacs and Elisp manuals describe the behavior of ARG as an
>     Drew> integer or a string.  But what about anything else?
> 
>     Drew> In `startup.el', `edt-mapper.el', and `tpu-edt.el', for example, we 
> find
>     Drew> (kill-emacs t).  How is someone to understand this code?
> 
> Itʼs equivalent to exit'ing with EXIT_SUCCESS, without having to worry
> about the value of '0' on your platform :-) Not sure how weʼd express
> that in the docstring.

I've documented it now, thanks.