added remark on unused modules

pb_utils/README.md

@@ -20,7 +20,11 @@ cd /mnt
 ./build_kernel.sh
 ```
 
-## chroot into debian rootfs to build test modules
+## ~~chroot into debian rootfs to build test modules~~
+> This is historical information, please note that this uses kernel threads.
+> Our perf events are currently configured not to count kernel space.
+> **This and possibly other changes cause this not to work**. We are using pb_submitter for testing.
+
 run `./chroot_image.sh`, this drops you in a shell on the created debian and run
 
 ```bash