Wish: message sequence chart in How it works

[stappersg]

Please add a message sequence chart to https://eternalterminal.dev/howitworks/

Possible tool for generating a msc is http://www.mcternan.me.uk/mscgen/

[stappersg]

I think that a msc will help in solving issues like #386

[jwmcglynn]

I added protocol docs and sequence diagrams in #523