doc: Added initial titlepage for the NED documentation

Author: rhornig

src/simu5g-index.ned

@@ -0,0 +1,13 @@
+//
+// Copyright (C) 2010 OpenSim Ltd.
+//
+// SPDX-License-Identifier: LGPL-3.0-or-later
+//
+
+
+//
+// @titlepage
+//
+// <center><h1>Simu5G Framework NED Documentation</h1></center>
+
+package simu5g;