To build:
make BOARD=ESPRUINO_PICO
To deploy: short the BOOT0/BTN contact on the back of the board (eg by
drawing over it with a graphite pencil), then hold down BTN while
inserting the board into the USB port. The board should then enter DFU
mode, and the firmware can be downloaded using:
make BOARD=ESPRUINO_PICO deploy
Damien George