Voice Bonnet drivers not installed (HACKING.md instructions)

[LRitzdorf]

The AIY Projects docs list the following drivers for the Voice Bonnet (v2) module:

MCU driver: modinfo aiy-io-i2c
MCU PWM driver: modinfo pwm-aiy-io
MCU GPIO driver: modinfo gpio-aiy-io
MCU ADC driver: modinfo aiy-adc

However, none of these are installed after following the instructions in the latest HACKING.md. Instructions of some sort should be added to cover this setup step, as sound does not work properly without it.

(The lack of these drivers was verified with the modinfo command, as shown in the quote above, and also by comparing dmesg output with a fresh install of the official AIY Projects OS release, where sound does work as expected.)

[LRitzdorf]

Update: Installing the aiy-dkms package (via apt) does provide the proper drivers, and dmesg output matches that of the AIY OS image. This should be added to HACKING.md.