Bug 22875: Document verbose option in import_patrons

Docs did not state that verbose can be repeated or that you
need more than 1 repetition to see lines that have failed

To test:
- Run ./import_patrons.pl -h
- Verify the additional documentation for -v is shown.

Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>

Signed-off-by: Nick Clemens <nick@bywatersolutions.com>

misc/import_patrons.pl

@@ -138,6 +138,12 @@ Retain extended patron attributes for existing patrons being overwritten
 
 Be verbose
 
+Multiple -v options increase the verbosity
+
+2 repetitions or above will report lines in error
+
+3 repetitions or above will report feedback
+
 =back
 
 =cut