Bug 17429: document the --plack/--noplack options of koha-list

Bug 17429: document the --plack/--noplack options of koha-list

The man page of koha-list does not list the --plack and --noplack
options.

This patch fixes that.

Test plan:

1) View the current man page for `koha-list` (with `man koha-list`)
   and notice how the --plack and --noplack options are missing.

2) Apply this patch.

3) Run the following command to re-generate the man page:

   xsltproc /usr/share/xml/docbook/stylesheet/docbook-xsl/manpages/docbook.xsl \
   debian/docs/koha-list.xml

   View the manual page again (with `man -l koha-list.8`), the
   two options are now displayed under SYNOPSIS and OPTIONS.

4) Make sure this test passes:
   prove -v xt/verify-debian-docbook.t

Signed-off-by: Mazen Khallaf <mazen.i.khallaf@gamil.com>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>