added ht as a flake output

[MatrixManAtYrService]

Having this as an output is handy because now I can put it in my devshell like so:

# flake.nix
{
  inputs = {
    nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
    flake-utils.url = "github:numtide/flake-utils";
    ht.url = "github:MatrixManAtYrService/ht";
  };
  outputs = { self, nixpkgs, flake-utils, ht }:
    flake-utils.lib.eachDefaultSystem (system:
      let
        pkgs = import nixpkgs {
          inherit system;
        };
      in
      {
        devShells.default = pkgs.mkShell {
          buildInputs = [
            ht.packages.${system}.ht
          ];
        };
      });
}

It works on MacOS, I'll un-draft it once I've tested it on Linux