Bug 31964: add a man page for koha-z3950-responder

Bug 31964: add a man page for koha-z3950-responder

The koha-z3950-responder command does not have a man page.

This patch fixes that.

Test plan:

1) Apply this patch.

2) Run the following command to generate the new man page:

   xsltproc /usr/share/xml/docbook/stylesheet/docbook-xsl-ns/manpages/docbook.xsl debian/docs/koha-z3950-responder.xml

3) View the generated man page with `man -l koha-z3950-responder.8`

   (KTD users may need to `apt-get install man-db` first as
   that package provides tools for reading manual pages)

4) Make sure this unit test passes:

   prove -v xt/verify-debian-docbook.t

Signed-off-by: Pedro Amorim <pedro.amorim@ptfs-europe.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>