Documentation Update: No more pi users

[chicagoandy]

New Raspberry Pi OS installs no longer have the default 'pi' user available.

It'd be helpful if you could include in your documentation the config changes necessary as a result of that change.

[geerlingguy]

@chicagoandy - For my own Pis, I normally flash them with Raspberry Pi Imager, and I have them create a pi user by default.

But the only thing you'd really need to change is in the kiosk.service file:

https://github.com/geerlingguy/pi-kiosk/blob/master/kiosk.service#L9-L12

Change all those values to your own username instead of pi.