Bug 29456: Add Hold_Reminder description to patron categories overview page

Bug 29456: Add Hold_Reminder description to patron categories overview page

This was missed when initially adding the notice.

To test:
- Go to Administraiton > patron categories
- Edit a patron category and check "Hold reminder" in messaging
  preferences, save.
- Go to the overview page and verify it shows as 'Unknown'.
- Apply patch.
- Descrpition should now display.

Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>