added nix dev environment.

flake.nix

@@ -0,0 +1,22 @@
+{
+  description = "hugo development environment";
+
+  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 = import nixpkgs {inherit system;};
+    in
+      with pkgs; {
+        devShells.default = mkShell {
+          buildInputs = [hugo];
+        };
+      });
+}