Add instructions to use a headless Raspberry PI for building and programming

[milelo]

Add instructions to use a headless Raspberry PI for building and programming. I've used this configuration in workshops. I gave students their own accounts on the PI. They can potentially SSH into the PI server from their own laptops and edit, build and flash-program on the PI. With newer versions of the PI they could also use VSCode Remote from their laptops to work on the PI. This minimise the setup required in workshops and makes client side machine-agnostic.