RPI Pico WebUSB Example

This is really just the example code from pico-sdk/lib/tinyusb/examples/device/webusb_serial made into its own project.

git clone https://github.com/nickzoic/rpi-pico-webusb.git
cd rpi-pico-webusb.git
git submodule update --init --recursive
make

# mount the device then copy the firmware
cp build/firmware.uf2 /media/$USER/RPI-RP2/

See also https://github.com/raspberrypi/tinyusb/issues/3