USB OTG serail support

[umgefahren]

I really like this repository! Helped me a lot.

However I can't log into the raspberry pi with a monitor, so I can't find out the IP address. Would it be possible to add an example how enable USB OTG serial?

Things i found:

• https://github.com/illegalprime/nixos-on-arm/blob/master/machines/raspberrypi-zero/otg.nix
• https://github.com/NixOS/nixos-hardware/blob/master/raspberry-pi/4/dwc2.nix

I haven't been able to figure it out by myself. Maybe you have better luck. (it's also quite hard to debug without a monitor)

[plmercereau]

Hello,
I love the idea; that would be a great addition. I don't have much time to spare in the upcoming weeks, so don't wait for this repo to implement this solution. Maybe someone else will have the time and skills for a pull request?