Merge pull request #38 from dart-lang/devoncarew-patch-1

Update CONTRIBUTING.md
diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index 615b92f..2632963 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -38,11 +38,9 @@
 
 ### File headers
 
-All files in the project must start with the following header.
-
-    // Copyright (c) 2017, 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.
+When creating new source files, please copy the file header from 
+https://github.com/dart-lang/clock/blob/master/lib/clock.dart and update the year
+for the copyright to the current year.
 
 ### The small print