Support mermaid diagrams?

[lidel]

We already use them on GitHub and docs.ipfs.tech,
They can be placed inside a markdown block, render as SVG, there is user-friendly editor/sandbox etc.

```mermaid
  graph TD;
      A-->B;
      A-->C;
      B-->D;
      C-->D;
```

Ref.

• https://github.blog/2022-02-14-include-diagrams-markdown-files-mermaid/
• https://mermaid-js.github.io/mermaid/
  • https://mermaid-js.github.io/mermaid-live-editor/

cc @darobin @hacdias (i remember @autonome suggested that before but can't find that convo now)