[Documentation] Unify docs into new material mkdocs

[fjp]

The two web pages, fjp.at/projects/diffbot (old) and fjp.at/diffbot are not always up to date with the latest docs in this github repository.

• Check if it is possible to add a github action to build the mkdocs automatically everytime a push is made. -> Works using this action yml.
• Move content from old docs fjp.at/projects/diffbot to new mkdocs.
  • Clicking on "Raspberry Pi Setup" on Diffbot website goes to "ROS Network Setup," not the correct page.

Originally posted by @fjp in ros-mobile-robots/diffbot#23 (comment)