Admittedly the first sentence in the README.md points to relevant information (http://setosa.io/ev/) However, yes, they should have included the one sentence description on that page it links to in the README.md itself.

Explained Visually (EV) is an experiment in making hard ideas intuitive inspired the work of Bret Victor's Explorable Explanations. See http://worrydream.com/ExplorableExplanations/ to learn more about Explorable Explanations.

See "Media for Thinking the Unthinkable" (Bret Victor, 2013) https://vimeo.com/67076984 and videos from https://vimeo.com/worrydream/videos for more context. Also, http://explorableexplanations.com (by Nicky Case) is a.... page that exists.