Update README and add contrib dir

contrib/real-device/helper/real-device-helper.cc

@@ -0,0 +1,8 @@
+#include "real-device-helper.h"
+
+namespace ns3
+{
+
+/* ... */
+
+}

contrib/real-device/helper/real-device-helper.h

@@ -0,0 +1,16 @@
+#ifndef REAL_DEVICE_HELPER_H
+#define REAL_DEVICE_HELPER_H
+
+#include "ns3/evb-lan9668.h"
+
+namespace ns3
+{
+
+// Each class should be documented using Doxygen,
+// and have an \ingroup real-device directive
+
+/* ... */
+
+}
+
+#endif /* REAL_DEVICE_HELPER_H */