Add nix devshell config

Author: Steven Bazyl

.envrc

@@ -0,0 +1,4 @@
+#!/usr/bin/env bash
+# the shebang is ignored, but nice for editors
+
+use flake .

flake.nix

@@ -0,0 +1,21 @@
+{
+  inputs = {
+    nixpkgs.url = "github:NixOS/nixpkgs/698fd43e541a6b8685ed408aaf7a63561018f9f8";
+    utils.url = "github:numtide/flake-utils";
+  };
+
+  outputs = { self, nixpkgs, utils }:
+    utils.lib.eachDefaultSystem (system:
+      let
+        pkgs = import nixpkgs { inherit system; };
+      in
+      {
+        devShell = with pkgs; mkShell {
+          buildInputs = [
+            nodejs_22
+            nodePackages.prettier
+          ];
+        };
+      }
+    );
+}