added package derivation for astronaut theme

modules/astronaut/derivation.nix

@@ -0,0 +1,45 @@
+# see also: https://github.com/xhos/nixdots/blob/main/derivs/sddm-astronaut-theme.nix
+{ pkgs, lib, theme ? "astronaut", themeOverrides ? null, ... }:
+let
+    overwriteConfig = (pkgs.formats.ini {}).generate "${theme}.conf.user" { General = themeOverrides; };
+in pkgs.stdenv.mkDerivation rec {
+    pname = "sddm-astronaut-theme";
+    version = "11c0bf6147bbea466ce2e2b0559e9a9abdbcc7c3";
+    dontBuild = true;
+
+    src = pkgs.fetchFromGitHub {
+        owner = "Keyitdev";
+        repo = "sddm-astronaut-theme";
+        rev = version;
+        hash = "sha256-gBSz+k/qgEaIWh1Txdgwlou/Lfrfv3ABzyxYwlrLjDk=";
+    };
+
+    dontWrapQtApps = true;
+
+    installPhase = ''
+        runHook preInstall
+
+        themeDir="$out/share/sddm/themes/astronaut"
+        mkdir -p "$themeDir"
+        cp -r "." "$themeDir"
+
+        mkdir -p "$out/share/fonts"
+        cp -r "$themeDir/Fonts/." "$out/share/fonts"
+
+        substituteInPlace "$themeDir/metadata.desktop" \
+            --replace "ConfigFile=Themes/astronaut.conf" "ConfigFile=Themes/${theme}.conf"
+
+        ${lib.optionalString (lib.isAttrs themeOverrides) ''
+            cp ${overwriteConfig} "$themeDir/Themes/${theme}.conf.user"
+        ''}
+
+        runHook postInstall
+    '';
+
+    meta = with lib; {
+        description = "Series of modern looking themes for SDDM.";
+        homepage = "https://github.com/Keyitdev/sddm-astronaut-theme";
+        license = licenses.gpl3;
+        platforms = platforms.linux;
+    };
+}