Bug 10119: Add note about CalculateFinesOnReturn to description of finesmode

Bug 10119: Add note about CalculateFinesOnReturn to description of finesmode

This adds a note to the descrpition of the finesmode system
preference mentioning that CalculateFinesOnReturn is another
option for charging fines:

Note: Fines can also be charged by the CalculateFinesOnReturn system preference.

To test:
- Search for the finesmode system preference
- Verify the new text shows and is correct

NOTE: New text appears as expected. You can also just scroll for
      it on the Circulation preferences tab.

Signed-off-by: Mark Tompsett <mtompset@hotmail.com>
Signed-off-by: Jonathan Druart <jonathan.druart@koha-community.org>
Signed-off-by: Tomas Cohen Arazi <tomascohen@unc.edu.ar>