Updated usage line with -f flag

bin/mkexec.pl

@@ -62,7 +62,7 @@ if (exists $bangs->{$type}) {
 ## '''' ##   ..............................................................-'
 
 sub usage {
-    print STDERR "usage: $0 filename [type]\n";
+    print STDERR "usage: $0 [-f] filename [type]\n";
     exit 0;
 }