This is a flake for installing lde from its Github releases, not for building it. It can be consumed in your flake as follows:

{
  # Latest release
  inputs.lde.url = "github:lde-org/lde-nix";
  # Pinned version, here for instance v0.8.1
  inputs.lde.url = "github:lde-org/lde-nix?ref=refs/tags/v0.8.1";
  # Nightly build, may not work depending on the maintainer's reactivity
  inputs.lde.url = "github:lde-org/lde-nix/nightly";
}

Then, add lde.packages.${your-system}.default wherever you install packages (assuming you added lde as an argument to your flake output), your-system being the architecture you run on.