Documentation fixes
Added more elaborate comments and descriptions
diff --git a/include/mbedtls/pk_internal.h b/include/mbedtls/pk_internal.h
index 06475e9..0a33087 100644
--- a/include/mbedtls/pk_internal.h
+++ b/include/mbedtls/pk_internal.h
@@ -3,7 +3,10 @@
*
* \brief Public Key cryptography abstraction layer: built-in key types
*
- * Copyright (C) 2006-2017, ARM Limited, All Rights Reserved
+ * This file contains built-in types for handling various key types using
+ * the interface defined in pk_info.h.
+ *
+ * Copyright (C) 2006-2018, ARM Limited, All Rights Reserved
* SPDX-License-Identifier: Apache-2.0
*
* Licensed under the Apache License, Version 2.0 (the "License"); you may