Update README.md and HACKING.md and resulting yak shave.

sky/tests/services/iframe-embed-vmc.sky

 <sky>
 
 <iframe></iframe>
 
 <script>
 import 'dart:async';
 import 'dart:sky';
 import 'dart:sky.internals' as internals;
 import 'dart:typed_data';
 
 import 'package:mojo/application.dart';
 import 'package:mojo/bindings.dart';
 import 'package:mojo/core.dart';
 import 'package:mojom/mojo/shell.mojom.dart' as shell_mojom;
 import 'package:mojom/mojo/input_events.mojom.dart' as input_events;
 import 'package:mojom/mojo/view_manager.mojom.dart' as view_manager;
-
-// This include is a hack which only works with sky_server.  For this to work
-// in the sky_sdk, this echo_service would need to make its own dart package.
-import '/gen/services/js/test/echo_service.mojom.dart' as echo_service_mojom;
+import 'package:mojom/mojo/echo_service.mojom.dart' as echo_service_mojom;
 
 class IFrameEmbed extends Application {
   IFrameEmbed.fromHandle(MojoHandle handle) : super.fromHandle(handle);
   IFrameEmbed(MojoMessagePipeEndpoint endpoint) : super(endpoint);
 
   void initialize(List<String> args, String url) {
     // The vmcApp provides ViewManagerClient and EchoService.
     const vmcURL =
         "http://127.0.0.1:8000/sky/tests/services/resources/iframe-vmc.js";
     final vmcAppConnection = connectToApplication(vmcURL);
@@ skipping 18 matching lines @@
 
 main() {
   var messagePipe = new MojoMessagePipe();
   var app = new IFrameEmbed(messagePipe.endpoints[1]);
   var shellProxy = new shell_mojom.ShellProxy.fromHandle(
       new MojoHandle(internals.takeShellProxyHandle()));
   app.initializeFromShellProxy(shellProxy, [], "");
 }
 </script>
 </sky>