feat: initial flake setup with flake-parts

Sets up a basic flake with flake-parts for modularity.

flake.nix

@@ -0,0 +1,20 @@
+{
+  inputs = {
+    # nixos-unstable provides a binary cache for all packages.
+    nixpkgs.url = "github:nixos/nixpkgs/nixos-unstable";
+    # flake-parts lets us define flake modules.
+    flake-parts.url = "github:hercules-ci/flake-parts";
+  };
+
+  outputs =
+    inputs@{ self, ... }:
+    inputs.flake-parts.lib.mkFlake { inherit inputs; } {
+      imports = [ inputs.flake-parts.flakeModules.modules ];
+      systems = [ "x86_64-linux" ];
+      perSystem =
+        { pkgs, ... }:
+        {
+          packages.default = pkgs.hello;
+        };
+    };
+}