Update bitflip.c
diff --git a/etc/bitflip.c b/etc/bitflip.c
index 9ddc48d..298595e 100644
--- a/etc/bitflip.c
+++ b/etc/bitflip.c
@@ -1,4 +1,6 @@
+// If it wasn't obvious, you're expected to compile this with UBSan and ASan.
+
#include <stdio.h>
#include <stdlib.h>
#include <signal.h>
