SBC-specific boot troubleshooting and notes

[MichaIng]

E.g. Odroid C4/HC4 loads the petitboot bootloader from internal SPI first, if present, which then might fail when the image has changed. So assure that the intended bootloader from the FAT partition is loaded, one needs to erase petitboot from the SPI: https://forum.odroid.com/viewtopic.php?p=323538#p323538

There are a few other examples, like SBCs with switches that define the boot mode and such. Probably easiest is to add another tabbing into the install on SBC tab which contains known device specific notes or troubleshooting instructions.