Add Nix flake

flake.nix

@@ -0,0 +1,15 @@
+{
+  inputs = {
+    devshell.inputs.nixpkgs.follows = "nixpkgs";
+    devshell.url = "github:numtide/devshell";
+    flake-parts.url = "github:hercules-ci/flake-parts";
+    import-tree.url = "github:vic/import-tree";
+    nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
+  };
+
+  outputs =
+    inputs:
+    inputs.flake-parts.lib.mkFlake { inherit inputs; } {
+      imports = [ (inputs.import-tree ./flake-modules) ];
+    };
+}