How to install Mermaid to render flowcharts in markdown?

I'm trying to render a flowchart in a markdown file using Mermaid. I have a ReadMe.md file in my GitHub repository, and I'd like to include a basic flowchart to help describe the contents. But I can't figure out how to get it to work. Would someone be able to post some more specific instructions on how to render a simple example?

In this link (https://unpkg.com/mermaid@8.0.0-rc.8/README.md), there's an example code snippet for the Mermaid installation:

    ```
    https://unpkg.com/mermaid@7.1.0/dist/
    ```

I included that code, then tried to make the flowchart in the next code snippet:

    ```
    graph TD;
        A-->B;
        A-->C;
        B-->D;
        C-->D;
    ```

But all it does is print that text out in the markdown file when I preview it.

It seems like it's possible based on the Mermaid ReadMe: https://github.com/knsv/mermaid/blob/master/README.md. But when I looked at the code it's actually a picture of the flowchart, not a rendering of code. So maybe what I'm asking isn't possible?

Would appreciate any help!