Update README and add contrib dir

contrib/traffic-generator/model/traffic-generator.h

@@ -0,0 +1,20 @@
+#ifndef TRAFFIC_GENERATOR_H
+#define TRAFFIC_GENERATOR_H
+
+// Add a doxygen group for this module.
+// If you have more than one file, this should be in only one of them.
+/**
+ * \defgroup traffic-generator Description of the traffic-generator
+ */
+
+namespace ns3
+{
+
+// Each class should be documented using Doxygen,
+// and have an \ingroup traffic-generator directive
+
+/* ... */
+
+}
+
+#endif /* TRAFFIC_GENERATOR_H */