Adding README.chromium.

Review URL: http://webrtc-codereview.appspot.com/252001/

git-svn-id: http://libyuv.googlecode.com/svn/trunk@49 16f28f9a-4ce2-e073-06de-1de4eb20be90

README.chromium

+Name: libyuv
+URL: http://code.google.com/p/libyuv/
+Version: 48
+License: BSD
+License File: LICENSE
+
+Description:
+libyuv is an open source project that includes
+YUV conversion and scaling functionality.