The docs are still a bit… ummm… todo: https://github.com/nix-community/disko/blob/713eb78002e69bd77f5a69595756fd2e564233f3/docs/reference.md
Give them time The examples plus some educated trial and error worked pretty well for me.
nix build github:nix-community/disko#disko-doc xdg-open ./result/index.html
I think this may be a good supplement, but it is still not perfect.
At least it doesn’t redirect you to Rickroll or worse