Render graph using mermaid.js in .md files

Hello,

In Github, we can use mermaid.js to render graph with code block.

for instance, if I write, 

```
flowchart LR

A ---> B
```
using ```mermaid at the begining of my code block, I can render a graph like below

```mermaid
flowchart LR

A ---> B
```

I search how to do it with gitiles markdown, but I don't think it' possible.

do someone have an idea how to do it ?