unix man pages HTML references?

[teuben]

During the HTML build of NEMO's man pages, which happens in the
cd $NEMO/man ; make docs
step, it uses links to the NEMO man html page, but there is no official reference to the unix ones'

However, there is at least one (and possible more root URL's) where they live, e.g.

https://man7.org/linux/man-pages/man1/ls.1.html

there must be a way in make-man.csh to add those?