Markdown mermaid support

[Stratis-Dermanoutsos]

So, I am using the documentation template for a personal documentation page.

I noticed that the markdown pages do not support mermaid code blocks.

Specifically, the CMD logs:

The language "mermaid" doesn't exist, falling back to plaintext.

Example:

```mermaid
 graph TD;
   a-->b;
   b-->c;
   c-->d;
\```

The ` is escaped here for GitHub to correctly format the text. I did not escape the code block in the actual code.

I know this is a very minor feature but it'd be very helpful to have.

[stereobooster]

Do you expect code highlighting or it being transformed to a diagram?