Consider using mermaid diagrams instead of graphviz

[Bisaloo]

E.g., to replace:

flowchart LR
    S -->|"infection<br>(transmission rate &beta;)"| E
    E -->|"onset of infectiousness<br>(infectiousness rate &alpha;)"| I
    I -->|"recovery<br>(recovery rate &gamma;)"| R

flowchart LR
    S -->|"infection<br>(transmission rate &beta;)"| E
    E -->|"onset of infectiousness<br>(infectiousness rate &alpha;)"| I
    I -->|"recovery<br>(recovery rate &gamma;)"| R

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This will allow a better integration with varnish (carpentries/varnish#125). In particular, colour theme will be respected & text can be selected.

[avallecam]

search engine: https://github.com/search?q=repo%3Aepiverse-trace%2Ftutorials-late%20DiagrammeR%3A%3AgrViz&type=code