update copyright text

rather than symlink the webm/vpx terms, use the same header as libvpx to
reference in-tree files

based on the discussion in:
https://codereview.chromium.org/12771026/

Change-Id: Ia3067ecddefaa7ee01550136e00f7b3f086d4af4
diff --git a/examples/webpmux.c b/examples/webpmux.c
index c88a054..bccd5c6 100644
--- a/examples/webpmux.c
+++ b/examples/webpmux.c
@@ -1,8 +1,10 @@
 // Copyright 2011 Google Inc. All Rights Reserved.
 //
-// This code is licensed under the same terms as WebM:
-//  Software License Agreement:  http://www.webmproject.org/license/software/
-//  Additional IP Rights Grant:  http://www.webmproject.org/license/additional/
+// Use of this source code is governed by a BSD-style license
+// that can be found in the COPYING file in the root of the source
+// tree. An additional intellectual property rights grant can be found
+// in the file PATENTS. All contributing project authors may
+// be found in the AUTHORS file in the root of the source tree.
 // -----------------------------------------------------------------------------
 //
 //  Simple command-line to create a WebP container file and to extract or strip