It might make sense to link to the repository with Jupiter notebook, https://github.com/mapio/programming-with-escher in the rendered output for the convenience of the reader. If the repository points to the rendered output, well Escher.
Actually it is, at the end of the first section https://mapio.github.io/programming-with-escher/#Programming... the sentence reads: "The source notebook is available on GitHub (under GPL v3), feel free to use issues to point out errors, or to fork it to suggest edits.
Square Limit and tiles."