There's a bug on the site, if you click "files" then scroll down and click one of the links under "Further Information", you get a 404
The README.md file is the homepage. It is intended to be displayed using the URL https://wapp.tcl.tk/index.html/doc/trunk/README.md and the hyperlinks are relative to that URL. When you click on the File menu, it shows the README.md file using a different URL - http://wapp.tcl.tk/index.html/dir?ci=tip - and the hyperlinks don't work for that URL.
Perhaps the right solution is to rename the README.md file to something different so that it is not displayed by default from the Files menu...