Update README and add contrib dir

contrib/tsn/model/clock-virtual.cc

@@ -0,0 +1,77 @@
+#include "clock-virtual.h"
+
+#include "ns3/log.h"
+#include "ns3/simulator.h"
+#include "ns3/uinteger.h"
+#include <ns3/double.h>
+
+namespace ns3
+{
+
+NS_LOG_COMPONENT_DEFINE("VirtualClock");
+
+NS_OBJECT_ENSURE_REGISTERED(VirtualClock);
+
+TypeId
+VirtualClock::GetTypeId()
+{
+    static TypeId tid =
+        TypeId("ns3::VirtualClock")
+            .SetParent<Clock>()
+            .SetGroupName("tsn")
+            .AddConstructor<VirtualClock>();
+    return tid;
+}
+
+
+VirtualClock::VirtualClock()
+{
+    NS_LOG_FUNCTION(this);
+}
+
+VirtualClock::~VirtualClock()
+{
+    NS_LOG_FUNCTION(this);
+}
+
+void
+VirtualClock::SetRefClock(Ptr<Clock> refClock)
+{
+  NS_LOG_FUNCTION(this);
+  m_refClock = refClock;
+}
+
+
+Time
+VirtualClock::GetLocalTime()
+{
+  NS_LOG_FUNCTION(this);
+  return GetUncorrectedLocalTime() + m_correctionOffset;
+}
+
+Time
+VirtualClock::GetUncorrectedLocalTime()
+{
+  NS_LOG_FUNCTION(this);
+
+  NS_ASSERT_MSG(m_refClock != nullptr,
+            "Reference clock no set using void VirtualClock::SetRefClock(Ptr<Clock> refClock)");
+  return m_refClock->GetUncorrectedLocalTime();
+}
+
+Time
+VirtualClock::GetTimeAt(Time t)
+{
+  NS_LOG_FUNCTION(this);
+  return m_correctionOffset + m_refClock->GetTimeAt(t);
+}
+
+Time
+VirtualClock::GetDuration(Time d)
+{
+  NS_LOG_FUNCTION(this);
+  return  m_refClock->GetDuration(d);
+}
+
+
+}