- Added Doxygen source code documentation parts (donated by Fox-IT)

diff --git a/include/polarssl/bignum.h b/include/polarssl/bignum.h
index 80399a2..79bc354 100644
--- a/include/polarssl/bignum.h
+++ b/include/polarssl/bignum.h
@@ -1,6 +1,8 @@
 /**
  * \file bignum.h
  *
+ * \brief  Multi-precision integer library
+ *
  *  Copyright (C) 2006-2010, Brainspark B.V.
  *
  *  This file is part of PolarSSL (http://www.polarssl.org)