Move hardware docs to main docs repo
We now have a top-level section 'Boards and Modules' for the hardware docs. Move the Pi-Tron CM4 docs there and keep only the software guides and examples. Reorganize those to a single navigation level.
See also: https://git.kontron-electronics.de/sw/ked/docs/docs/-/merge_requests/13
Edited by Frieder Schrempf