Add/correct missing command line options in help text

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/init.c b/init.c
index 1d3ee40..f5dff50 100644
--- a/init.c
+++ b/init.c
@@ -774,6 +774,7 @@
 	printf("\t--showcmd\tTurn a job file into command line options\n");
 	printf("\t--eta=when\tWhen ETA estimate should be printed\n");
 	printf("\t          \tMay be \"always\", \"never\" or \"auto\"\n");
+	printf("\t--readonly\tTurn on safety read-only checks, preventing writes\n");
 }
 
 #ifdef FIO_INC_DEBUG