Update README.md

Author: StuartIanNaylor

README.md

@@ -66,6 +66,8 @@ log     lz4     20M             60M             /var/log                /log.bin
 ```
 Zram-config also allows a 'kiosk mode' where `sudo zram-config enable-ephemeral` on reboot will load the whole root into a ro OverlayFS with zram writeable upper. 
 `sudo zram-config disable-ephemeral` and reboot to return to a normal system.
+You may need to reboot after the rpi-update and then mkinitramfs -o /boot/initrd as a newer kernel maybe updated.
+Check the 'Without NFS' section of https://blockdev.io/read-only-rpi/
 
 
 ### It is working?