Building the epub myself on Ubuntu was an involved (but educational) experience. As the guide in the Github repo says, you need to install Pandoc and Calibre.

Building the epub myself on Ubuntu was an involved (but educational) experience. As the guide in the Github repo says, you need to install Pandoc and Calibre. However, you also need ImageMagick, which is not mentioned in the guide. You also need XeLaTeX, which has the package name texlive-xetex instead of just xelatex, for some reason. pdfunite requires poppler-utils.