suffix other than index.html to be declared. E.g. if a build does
echo "doc manual $out manual.html" >> $out/nix-support/hydra-build-products
the default link for the product is
http://localhost:3000/build/417/download/1/manual.html
but other files are also accessible, e.g.
http://localhost:3000/build/417/download/1/style.css