bug#42325: 28.0.50; [PATCH] Incomplete keymap in Bookmark Menu mode description

[Eli Zaretskii]

> From: Matthias Meulien <orontee@gmail.com>
> Date: Sat, 11 Jul 2020 21:15:57 +0200
> 
> When one call describe-mode from *Bookmark List* buffer, the 
> displayed documentation for the Bookmark Menu major mode displays 
> an incomplete hard-coded keymap: The useful key / 
> (bookmark-bmenu-search) isn't listed. I propose to rely on 
> derived-mode-make-docstring to put the mode's keymap in mode 
> docstring and to remove the currently hardcoded keymap 
> description.

Thanks.

As Drew points out, there's no need to show the entire set of
commands, so I just added '/' to the list.