Add a flake and move code to index.tsx

flake.nix

@@ -0,0 +1,27 @@
+{
+  description = "Sample Nix ts-node build";
+  inputs = {
+    nixpkgs.url = "github:nixos/nixpkgs/nixos-unstable";
+    flake-utils.url = "github:numtide/flake-utils";
+    gitignore = {
+      url = "github:hercules-ci/gitignore.nix";
+      inputs.nixpkgs.follows = "nixpkgs";
+    };
+  };
+  outputs = {
+    self,
+    nixpkgs,
+    flake-utils,
+    gitignore,
+    ...
+  }:
+    flake-utils.lib.eachDefaultSystem (system: let
+      pkgs = import nixpkgs {inherit system;};
+      nodejs = pkgs.nodejs-18_x;
+    in
+      with pkgs; {
+        devShell = mkShell {
+          buildInputs = [nodejs yarn watchman alejandra nodePackages.prettier];
+        };
+      });
+}