brintOS nRF9151 SOM station

  openocd -f board/emcraft-som-nrf9151.cfg -c init -c "flash probe 0" -c shutdown
                                        probe the nRF9151 through the J-Link (SWD)
  som-console                           the board's shell (picocom; --list, --find)
  som-program-nrf91 --app asset_tracker_v2 --check
                                        probe the board; is the release compatible? writes nothing
  som-program-nrf91 --app asset_tracker_v2
                                        install release 2.0-122 (or --app hello_mcuboot)
  som-test-nrf91 --quick                firmware, watchdog, AT, modem firmware, SIM (read-only)
  brintos-selftest 99-nrf-station.test  check the station itself, no board needed

  /README.md                            what this machine is, and where things live
  /usr/share/brintos-nrf-station/       the guide: wiring, reads, what not to do
  /usr/share/brintos-som/nrf9151/       the release images, each with its PROVENANCE