add find_boot_keyboard function and example#7

tannewt merged 3 commits intoadafruit:mainadafruit/Adafruit_CircuitPython_USB_Host_Descriptors:mainfrom

FoamyGuy:find_boot_keyboardFoamyGuy/Adafruit_CircuitPython_USB_Host_Descriptors:find_boot_keyboardCopy head branch name to clipboard