add illustrations

[NickleDave]

@tlestang said he had images he uses in talks that could be appropriate

[NickleDave]

Turing Way has a bunch of images that are CC-BY and might be integrated into the flowchart
https://zenodo.org/record/4906004

[NickleDave]

e.g. https://the-turing-way.netlify.app/_images/first-pull-request.png