Add definition of purpose and use of networking module
The purpose of the networking module can sometimes be misunderstood. This adds
a definition and explanation of what the networking module is and what it can be
used for.
/**
* \file net_sockets.h
*
- * \brief Network communication functions
+ * \brief Network sockets abstraction layer to integrate Mbed TLS into a
+ * BSD-style sockets API.
+ *
+ * The network sockets module provides an example integration of the
+ * Mbed TLS library into a BSD sockets implementation. The module is
+ * intended to be both an example of how Mbed TLS can be integrated
+ * into a networking stack, and also act as Mbed TLS's integration on
+ * the supported platforms.
+ *
+ * The module is intended only for the use of the Mbed TLS library and
+ * is not intended to be used by third party application software.
+ *
+ * The supported platforms are as follows:
+ * * Microsoft Windows and Windows CE
+ * * POSIX/Unix platforms including Linux, OS X
+ *
*/
/*
* Copyright (C) 2006-2015, ARM Limited, All Rights Reserved
