Add welcome text for default template

flake.nix

@@ -8,6 +8,19 @@
         default = {
           description = "Default flake template";
           path = ./default;
+          welcomeText = ''
+            # Welcome to your new Nix flake ❄️🍁
+
+            To activate your new flake's development environment, run `nix develop` or `direnv allow` if you use direnv.
+
+            For a more interactive flake initialization experience, delete the `flake.nix` that was just created and use fh, the CLI for FlakeHub:
+
+                nix run "https://flakehub.com/f/DeterminateSystems/fh/0" -- init
+
+            For more on flakes, check out **Zero to Nix**, our flake-forward guide to Nix:
+
+                https://zero-to-nix.com
+          '';
         };
       };
     };