verify-pack: add --stat-only to the synopsis section

Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: gitster

Documentation/git-verify-pack.txt

@@ -8,7 +8,7 @@ git-verify-pack - Validate packed git archive files
 
 SYNOPSIS
 --------
-'git verify-pack' [-v|--verbose] [--] <pack>.idx ...
+'git verify-pack' [-v|--verbose] [-s|--stat-only] [--] <pack>.idx ...
 
 
 DESCRIPTION