Write complete guide to installing and configuring Raspbian on Pi

[TomGC96]

A provisioner exists for the RaspberryPi image (http://abersailbot.readthedocs.io/en/latest/provisioning.html), however this assumes that some things have been configured manually. It would be good to have a complete step-by-step guide to installing and configuring a fresh installation of Raspbian for Dewi.

This guide should be written by installing and configuring a fresh installation on the Pi and noting down all steps, to avoid missing any details.