bug#31445: Command c-toggle-comment-style should be described in emacs-26 manual.

[Eli Zaretskii]

> From: Takesi Ayanokoji <ayanokoji.takesi@gmail.com>
> Date: Mon, 14 May 2018 09:23:53 +0900
> 
> In doc/emacs/programs.texi lines 1696-1699 describes
> 
> You can toggle electric action with the command
> @kbd{C-c C-l}; when it is enabled, @samp{/@var{c}l} appears in the
> mode line after the mode name (where @var{c}, if present, is @samp{*}
> or @samp{/}):
> 
> This is written in the descriptions for c-toggle-electric-state. This 
> descriptions say about @var{c}, but I cannot
> found descriptions for it.
> 
> I think it should be described in this manual that what means @samp{*} or 
> @samp{/}.
> 
> But I understand this letter is about to command  c-toggle-comment-style.
> 
> So I think it should be tescribed in this manual's 'Comments' section(or 
> elsewhare appropriate)

This is CC Mode specific feature, and is fully described in the CC
Mode manual, a separate file.  I added a short explanation of what *
and / mean, and a cross-reference to the CC Mode manual.

Thanks.