The user's manual is created with gendoc. You'll have to download and compile that tool.
wget https://gitlab.com/bztsrc/gendoc/-/raw/main/gendoc.c
gcc gendoc.c -o gendoc
Simple as that. Once you have gendoc, you can create the manual by going into one of the language code directories and running
cd docs/en
gendoc ../../public/index.html manual.xml