README steps out of order, or at least need a note on process

[Rippert]

Hi, I just implemented your overlayfs on a Manjaro-Arm build on a RPi-3B. It works very well, but I did have to modify my process from your README slightly.

Since the Set filesystems readonly section comes after the Enable overlayroot in commandline section, and you call for a reboot between the two, the root fs is already an overlay, and any changes to it are lost on reboot. So editing the /etc/fstab file at that point is useless.

This can be fixed by telling installers to use the rwrootfs command before editing the /etc/fstab file, or just changing your instructions to not call for a reboot between the Enable overlayroot in commandline section and the Set filesystems readonly section.

Thanks,
Ted