nix: add flake

flake.nix

@@ -0,0 +1,38 @@
+{
+  description = "Ambroisie's blog";
+
+  inputs = {
+    futils = {
+      type = "github";
+      owner = "numtide";
+      repo = "flake-utils";
+      ref = "master";
+    };
+
+    # https://nixpk.gs/pr-tracker.html?pr=124808
+    nixpkgs = {
+      type = "github";
+      owner = "NixOS";
+      repo = "nixpkgs";
+      ref = "nixos-unstable";
+    };
+  };
+
+  outputs = { self, futils, nixpkgs } @ inputs:
+    futils.lib.eachSystem futils.lib.allSystems (system:
+      let
+        inherit (nixpkgs) lib;
+        pkgs = nixpkgs.legacyPackages.${system};
+      in
+      {
+        devShell = pkgs.mkShell {
+          name = "blog";
+
+          buildInputs = with pkgs; [
+            gnumake
+            hugo
+          ];
+        };
+      }
+    );
+}