Missing support for `mermaid` in markdown

[adamjosefus]

Github add support for mermaid in markdown (Github blog post).

Drawing charts and diagrams in readme is powerfull feature. Please add support to https://deno.land/x too.

[kidonng]

GitHub's markup feature sets are way more expansive than CommonMark or GFM. It's not practical to tell every platform rendering a Markdown file to become GitHub, especially given Mermaid is a relatively new supported and not so widely used format.

You already have the link to GitHub, so when deno.land is not capable, view on GitHub instead.

[crowlKats]

I am actually in favour of having mermaid support. @lucacasonato thoughts? Also gfm's description is "Server-side GitHub Flavored Markdown rendering for Deno", so supporting mermaid would only make sense.

[crowlKats]

Blocked on https://github.com/mermaid-js/mermaid/issues/3650