* followed https://wiki.postmarketos.org/wiki/PINE64_PineNote_(pine64-pinenote)
* except for flashing:
    * dd root.img to /dev/mmcblk0p6
    * mount /dev/mmcblk0p6 to /mnt
    * mount boot.img and copy over files to /mnt/boot
    * change /etc/extconfig to use /boot subdir
* boot by selecting postmarketos