Bug 7988: Make note on authorized values page less confusing

Bug 7988: Make note on authorized values page less confusing

Nicole suggested a change of the note, that this patch is implementing:

NOTE: If you change an authorized value code, existing records
using it won't be updated. Changes to value descriptions will show
immediately.

To test:
- Go to administration > authorised values
- Check the note showing on the page
- Select a category from the pull down and edit an existing entry
- Check the note on this page is also correct

Patch behaves as expected.
Signed-off-by: Marc Véron <veron@veron.ch>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@gmail.com>