Write Uboot to SD-card example

  To prepare your SD-Card and flash-uboot using the Generic image
  As always: **Be sure you got the right device (/dev/.....) pointing to your sd-card**
  Replace X with your appropriate value
export sdcard="/dev/sdX"

  Write to SD-Card:
xzcat Nethserver-7.7.1908-RC1-Uboot-img.raw.xz | sudo dd of=${sdcard} status=progress bs=4M && sudo sync

  Mount your sd-card, mountpoint (/mnt) is arbitrary:
sudo mount ${sdcard}2 /mnt

  Find the available boardmodels: 
ls /mnt/usr/share/uboot/

  In this writeup _orangepi_plus2e_ is assumed
export boardmodel="orangepi_plus2e"

  Find name of u-boot file: 
ls /mnt/usr/share/uboot/${boardmodel}

  It turns-out out for orangepi_plus2e it is u-boot-sunxi-with-spl.bin 
export uboot="u-boot-sunxi-with-spl.bin"

  Write u-boot to sd-card:
sudo dd if=/mnt/usr/share/uboot/${boardmodel}/${uboot} of=${sdcard} bs=1024 seek=8 conv=fsync,notrunc

  Unmount sd-card: 
sudo umount /mnt

  Note other boards might need extra boodloaders in a setup as described by the vendor.