Docs - Flappy Bird Tutorial Suggestion - Add images at each step

[scottwestover]

For new game developers, when following along with the tutorial, it can be helpful to show an example of what the output should be for each step of the tutorial. This can help provide a quick visual validation that the code they are writing/copying is working as expecting.

It looks like for other parts of the docs site, static images are also included with the markdown files for examples, example: https://github.com/excaliburjs/Excalibur/blob/main/site/docs/00-z-quick-start.mdx

If the team would be open to this suggestion, I would be happy to submit pull request and relevant issue.