Add catppuccin theme for sddm

nixos/desktop/pkgs/sddm-catppuccin-macchiato.nix

@@ -0,0 +1,18 @@
+{ stdenv, fetchFromGitHub }:
+{
+  sddm-catppuccin-macchiato = stdenv.mkDerivation rec {
+    pname = "sddm-catppuccin-macchiato-theme";
+    version = "1.0";
+    dontBuild = true;
+    installPhase = ''
+      mkdir -p $out/share/sddm/themes
+      cp -aR $src/src/catppuccin-macchiato $out/share/sddm/themes/catppuccin-macchiato
+    '';
+    src = fetchFromGitHub {
+      owner = "catppuccin";
+      repo = "sddm";
+      rev = "bde6932e1ae0f8fdda76eff5c81ea8d3b7d653c0";
+      sha256 = "ceaK/I5lhFz6c+UafQyQVJIzzPxjmsscBgj8130D4dE=";
+    };
+  };
+}

nixos/desktop/sddm.nix

@@ -1,6 +1,13 @@
-{ ... }:
+{ pkgs, ... }:
+let
+  sddm-catppuccin-macchiato = pkgs.callPackage ./pkgs/sddm-catppuccin-macchiato.nix { };
+in
 {
   services.xserver.displayManager.sddm = {
     enable = true;
+    theme = "catppuccin-macchiato";
   };
+  environment.systemPackages = [
+    sddm-catppuccin-macchiato.sddm-catppuccin-macchiato
+  ];
 }