Specify the license of the documentation in the LICENSE file.

Added a mention that the license of the documentation is CC-BY-ND
and not Apache 2.0, as the other contents of the repository.

Change-Id: If74ac2abbff2d6eea10d0f1f17ef1f1cc60e98d9

LICENSE

@@ -1,4 +1,13 @@
-Apache License
+All parts, except the contents of the documentation directory, are licenced
+under Apache License v2.0. See the license text below.
+
+The documentation is licensed under Creative Commons CC-BY-ND 2.0
+(http://creativecommons.org/licenses/by-nd/2.0/legalcode).
+
+
+-----------------------------------------------------------------------------
+
+                                Apache License
                            Version 2.0, January 2004
                         http://www.apache.org/licenses/