Support for Mermaid Graphs in documentation

[tedivm]

What's the problem this feature will solve?

Mermaid is a diagramming system that allows diagrams to be defined in Markdown. It uses javascript to convert the text into an SVG. It is supported by Github, so any markdown on Github also supports mermaid.

Describe the solution you'd like

The QuasiQueue project uses Mermaid. The PyPi project just displays it as a codeblock, rather than a graph. It does render on Github. It would be nice if PyPi supported it since it would mean diagrams could be easily embedded in documentation.

Additional context

• Integration Documentation
• Existing Integrations

[di]

Duplicate of pypa/readme_renderer#223.