Explain zipcmp -t more.

src/zipcmp.c

diff --git a/src/zipcmp.c b/src/zipcmp.c
index ead0abd..6b6278b 100644
--- a/src/zipcmp.c
+++ b/src/zipcmp.c
@@ -102,7 +102,7 @@
   -i       compare names ignoring case distinctions\n\
   -p       compare as many details as possible\n\
   -q       be quiet\n\
-  -t       test zip files\n\
+  -t       test zip files (compare file contents to checksum)\n\
   -V       display version number\n\
   -v       be verbose (print differences, default)\n\
 \n\