Support mermaid diagrams?

We already use them on [GitHub](https://github.blog/2022-02-14-include-diagrams-markdown-files-mermaid/) and docs.ipfs.tech,
They can be placed inside a markdown block, render as SVG, there is user-friendly [editor/sandbox](https://mermaid-js.github.io/mermaid-live-editor/) 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)