Ensure CHANGELOG.md and README.md ship with sky, mojo, and mojom packages

sky/sdk/BUILD.gn

 # Copyright 2015 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import("//mojo/public/dart/rules.gni")
 
 dart_pkg("sdk") {
   sources = [
     "CHANGELOG.md",
+    "README.md",
     "bin/init.dart",
     "lib/assets/.gitignore",
     "lib/assets/material-design-icons.sha1",
     "lib/download_material_design_icons",
     "lib/framework/README.md",
     "lib/framework/animation/animated_value.dart",
     "lib/framework/animation/curves.dart",
     "lib/framework/animation/fling_curve.dart",
     "lib/framework/animation/generators.dart",
     "lib/framework/animation/mechanics.dart",
@@ skipping 104 matching lines @@
     "//sky/services/viewport",
   ]
 
   datadeps = [
     "//sky/services/testing:bindings",
     "//sky/engine/bindings",
   ]
 
   sdk_ext_directory = "$root_gen_dir/sky/bindings"
 }