Add basic NixOS shell.nix file

shell.nix

@@ -0,0 +1,13 @@
+with import <nixpkgs> {};
+stdenv.mkDerivation rec {
+  name = "env";
+  env = buildEnv { name = name; paths = buildInputs; };
+  buildInputs = [
+    elmPackages.elm
+    elmPackages.elm-format
+    go
+    golint
+    nodejs
+    swaks
+  ];
+}