Adding '--logfile' option description

--- ./main.c
+++ ./main.c
@@ -199,6 +199,7 @@ static void Usage( char *pName )
            "  --no-cleanup       Skip the cleanup stage at the end of running your script\n"
            "                       this may make your code run faster, but if you forget\n"
            "                       to close files then they will remain unflushed and unclosed\n"
+           "  --logfile          File to log PPerl debuging information\n"
     );
     exit( 1 );
 }