Support boilerplate for Elm clients

Lately I was toiling while writing a ClojureScript client. This made me crave
Elm. I'm going to rewrite the ClojureScript client using Elm, but along the way,
I'm stopping off here and recording my starter boilerplate.

boilerplate/elm/shell.nix

@@ -0,0 +1,9 @@
+let
+  pkgs = import <nixpkgs> {};
+in pkgs.mkShell {
+  buildInputs = with pkgs; [
+    elmPackages.elm
+    elmPackages.elm-format
+    elmPackages.elm-live
+  ];
+}