#11 Add some screenshots

https://pygame.org/project/3004/5138 has some screenshots. The problem is that [Gogs doesn't support RST files yet](https://github.com/gogits/gogs/issues/211). So even if I added screenshots, they wouldn't render in the README of the project.

[PyPI now supports Markdown](https://dustingram.com/articles/2018/03/16/markdown-descriptions-on-pypi)