To make the html documentation, install the prerequisites:

apt-get install python-sphinx texlive-latex-recommended dvipng librsvg2-bin imagemagick docbook2x

and do:

make html

and to view it, do:

epiphany _build/html/index.html

Fedora (and maybe other RPM based distributions), install the prerequisites:

dnf install python3-sphinx librsvg2 ImageMagick docbook2X texlive-dvipng-bin texlive-scheme-medium librsvg2-tools

After that, run:

make html

If you get mpmath error, install python3-mpmath package:

dnf install python3-mpmath

And view it at:

_build/html/index.html