Add license for bundled software

index.md

@@ -36,3 +36,16 @@ As default, PostgreSQL isn't capable for CJK full text search. You can use super
 PGroonga is released under [PostgreSQL license](http://opensource.org/licenses/postgresql) that is similar to BSD license and MIT license.
 
 See [COPYING](https://github.com/pgroonga/pgroonga/blob/master/COPYING) file for details such as copyright holders.
+
+Bundled software is released under different license. Here are bundled software and license information:
+
+  * [xxHash](https://github.com/Cyan4973/xxHash)
+    * BSD license
+    * Copyright: `Copyright (c) 2012-2014, Yann Collet`
+    * Detail: [`vendor/xxHash/LICENSE`](https://github.com/Cyan4973/xxHash/blob/master/LICENSE)
+
+  * [Groonga](http://groonga.org/) (bundled only for Windows package)
+    * LGPL 2.1
+    * Copyright: `Copyright(C) 2009-2015 Brazil`
+    * Detail: [`vendor/groonga/COPYING`](https://github.com/groonga/groonga/blob/master/COPYING)
+