added basic nix flake file.

flake.nix

@@ -0,0 +1,32 @@
+{
+  description = "Trying nest.js";
+  
+  inputs = {
+    nixpkgs.url = "nixpkgs/nixos-21.11";
+    flake-utils.url = "github:numtide/flake-utils";
+  };
+
+  outputs = { self, nixpkgs, flake-utils }: 
+
+    flake-utils.lib.eachDefaultSystem (system:
+      let pkgs = nixpkgs.legacyPackages.${system}; in
+      rec {
+        packages = flake-utils.lib.flattenTree {
+          hello = pkgs.hello;
+          gitAndTools = pkgs.gitAndTools;
+          nodejs = pkgs.nodejs;
+        };
+        defaultPackage = packages.hello;
+        apps.hello = flake-utils.lib.mkApp { drv = packages.hello; };
+        defaultApp = apps.hello;
+        devShell = pkgs.mkShell {
+          name = "Nid-JS";
+          buildInputs = with pkgs; [
+            nodejs
+            flyway
+            nodePackages.node2nix
+            ];
+        };
+      }
+    );
+}