Add Nix flake

Author: stancl

.gitignore

@@ -1 +1,2 @@
 /target
+/result

flake.lock

@@ -0,0 +1,36 @@
+{
+  description = "An intuitive system for organizing TODOs in code";
+
+  inputs = {
+    nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
+    flake-utils.url = "github:numtide/flake-utils";
+  };
+
+  outputs = { self, nixpkgs, flake-utils }:
+    flake-utils.lib.eachDefaultSystem (system:
+      let
+        pkgs = nixpkgs.legacyPackages.${system};
+      in
+        {
+          packages.default = pkgs.rustPlatform.buildRustPackage {
+            name = "todos";
+            src = pkgs.lib.cleanSource ./.;
+            cargoLock.lockFile = ./Cargo.lock;
+
+            meta = with pkgs.lib; {
+              description = "An intuitive system for organizing TODOs in code";
+              homepage = "https://github.com/archtechx/todo-system";
+              license = licenses.mit;
+            };
+          };
+
+          devShells.default = pkgs.mkShell {
+            buildInputs = with pkgs; [
+              cargo
+              rustc
+              clippy
+            ];
+          };
+      }
+    );
+}