Add notes to issue14236_source.dart on regenerating

tests/standalone/issue14236_source.dart

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 //
 // This is the original dart program that was used to generate the snapshot
 // in file issue14236_test.dart
 // The original test/main has been commented out and we have a test/main which
 // throws an error to ensure that this file is not executed as part of the
 // test.
+// 
+// When issue14236_test.dart fails, you must regenerate it using the VM 
+// with your changes. Notes on regenerating:
+// 1) Swap the test and main functions below.
+// 2) $ dart --snapshot=issue14236_test.dart issue14236_source.dart
+// 3) Undo changes in 1.
 
 library test.issue14236;
 import "dart:isolate";
 import "package:expect/expect.dart";
 import "package:async_helper/async_helper.dart";
 
 /*
 test(SendPort replyTo) {
   replyTo.send("from Isolate");
 }
 
 main() {
   asyncStart();
   ReceivePort port = new ReceivePort();
   Isolate.spawn(test, port.sendPort);
   port.first.then((msg) {
     Expect.equals("from Isolate", msg);
     asyncEnd();
   });
 }
 */
 
 test() {
   Expect.fail("Don't expect this to run at all");
 }
 main() {
   Expect.fail("Don't expect this to run at all");
 }