[pan] improve pan usage message

[Dominique Dumont <ddumont src gnome org>]

commit ee1e15bcf31a7a248ba5810e190a5d9ae739326e
Author: Dominique Dumont <dod debian org>
Date:   Sun Nov 7 16:06:16 2021 +0100

    improve pan usage message

 pan/gui/pan.cc | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)
---
diff --git a/pan/gui/pan.cc b/pan/gui/pan.cc
index eb6a315..60a1d16 100644
--- a/pan/gui/pan.cc
+++ b/pan/gui/pan.cc
@@ -635,7 +635,8 @@ _("General Options\n"
 "  -h, --help               Show this usage information and exit.\n"
 "  -v, --version            Print release version and exit.\n"
 "  --verbose                Be verbose (in non-GUI mode).\n"
-"  --debug                  Run in debug mode.\n"
+"  --debug                  Run in debug mode. (use --debug twice for verbose debug)\n"
+"  --debug-ssl              Run with TLS (aka ssl) debug mode.\n"
 "\n"
 "URL Options\n"
 /** NOT IMPLEMENTED