Added a defauld.nix file to build app on NixOS.

default.nix

@@ -0,0 +1,36 @@
+with import <nixpkgs> {};
+# { lib
+# , fetchPypi
+# , python3Packages
+# }:
+
+python3Packages.buildPythonApplication rec {
+  pname = "kalamine";
+  version = "0.37";
+  pyproject = true;
+
+  src = fetchPypi {
+    inherit pname version;
+    hash = "sha256-MdWP15d4J56ifLli01OIBZqgzpKQZf5f6OcR+3fP0zk=";
+  };
+
+  nativeBuildInputs = [
+    python3Packages.hatchling
+  ];
+
+  propagatedBuildInputs = with python3Packages; [
+    click
+    livereload
+    pyyaml
+    tomli
+    progress
+  ];
+
+  meta = with lib; {
+    description = "A cross-platform Keyboard Layout Maker";
+    homepage = "https://github.com/OneDeadKey/kalamine";
+    license = licenses.mit;
+    # maintainers = with maintainers; [ marsam ];
+    mainProgram = "kalamine";
+  };
+}