add rate adaptation example to demonstrate Minstrel operation

examples/wireless/wscript

@@ -63,3 +63,6 @@ def build(bld):
     
     obj = bld.create_ns3_program('power-adaptation-interference', ['core', 'mobility', 'wifi', 'applications', 'flow-monitor'])
     obj.source = 'power-adaptation-interference.cc'
+
+    obj = bld.create_ns3_program('rate-adaptation-distance', ['core', 'mobility', 'wifi', 'applications', 'flow-monitor'])
+    obj.source = 'rate-adaptation-distance.cc'