feat: nixos module is configurable now

assets/pkg/nix/get-cfg-file.nix

@@ -0,0 +1,13 @@
+{ cfg, src, lib, ... }:
+let
+    maker = import ./make-cfg.nix {
+        inherit lib;
+        keys-h-file = builtins.readFile "${src}/include/keys.h";
+    };
+in builtins.toFile "lidm.conf" (
+    if builtins.isString cfg
+        then builtins.readFile "${src}/themes/${cfg}.ini"
+    else if builtins.isAttrs cfg
+        then maker.make cfg
+    else builtins.throw "invalid cfg type, expected str or attrs"
+)