Bug 6681: (qa followup) document the existence of the sample files

Bug 6681: (qa followup) document the existence of the sample files

As requestedby people testing the patch, I add references to the new
xslt files on the Z39.50/SRU servers help.

Example usages are also provided.

Test:
- Apply the patch
- Go to the help page on the 'Z39.50/SRU Servers' page
=> SUCCESS: Notice there's a section documenting XSLT file(s) usage
            and provides some examples that cover the introduced files.
- Sign off

Thanks
Tomas

Sponsored-by: Universidad Nacional de Cordoba
Signed-off-by: Frederic Demians <f.demians@tamil.fr>
  Help page does shed some light to the XSLT usage. Enough to my taste.

Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Tomas Cohen Arazi <tomascohen@gmail.com>