Add helpful notes / guidance to K-means example page.

[mariemayadi]

(+ png image to im...g/quickstart-example)
Please notify if image was not properly uploaded.

[uce]

Thanks for taking care of this.

Instead of the image you can have the following Markdown syntax, which people can copy & paste:

    ```bash
    java -cp ...
    ```

This will result in something like:

java -cp ...