To build, you must have the Espressif IoT Development Framework (ESP-IDF)
installed. You can find it here:

https://docs.espressif.com/projects/esp-idf/en/latest/esp32/get-started/

Make sure you have sourced export.sh so the idf.py command runs correctly. Then
run these commands:

    idf.py set-target esp32
    idf.py menuconfig

Go to the "WiFi Configuration" menu and fill in the details matching your WiFi
network. Then build and flash with:

    idf.py build
    idf.py -p <serial port device> flash