The Lensfun website is based on Jekyll which is a static website generator. See http://jekyllrb.com/ for more information.
Basic instructions:
Install Ruby and its development packages
sudo apt-get install ruby ruby-dev nodejs
Install Jekyll
sudo gem install jekyll rdiscount
Run Jekyll to build the html files and serve the whole web site with a local web server at http://localhost:4000/
jekyll serve
All web content can be found in the _site/
subfolder and may be
packaged into the documentation or uploaded to any web server.
Use jekyll build
to only build without starting a local web server.