Add license and a very basic setup script I used to bootstrap the Feathers

BOARD_SETUP.md

@@ -0,0 +1,13 @@
+- Arch dependencies: adafruit-ampy python-dotenv wget
+- Optional Arch dependencies: picocom (serial interface)
+- `pip3 install --user adafruit nrfutil`
+- `mkdir feather_flashing && cd feather_flashing`
+- `git clone https://github.com/adafruit/Adafruit_nRF52_Bootloader.git && cd Adafruit_nRF52_Bootloader`
+- `make BOARD=feather_nrf52832 VERSION=2.0.1 SERIAL=/dev/ttyUSB0 dfu-flash` (no
+  root req)
+- `cd .. && git clone git@github.com:adafruit/circuitpython.git && cd circuitpython`
+- `git submodule update --init`
+- `make -C mpy-cross`
+- `cd ports/nrf`
+- `./drivers/bluetooth/download_ble_stack.sh`
+- `make BOARD=feather_nrf52832 SERIAL=/dev/ttyUSB0 dfu-gen dfu-flash`