ns3 introduce

??? Now you can find this file to be written in English .The following are reasons: ??? First,the ns3 simulator is a very new simulator,so there are a few people who are using it. ??? Then,if you write something in? English,it will be searched easily by google,and you can't serach it by baidu,so it may be better in English. ??? Third,i will write my paper in English,this can be look as a training. ??? In order to finish all of these,i decided to write my NS-3 in English. ??? I am happy to see your words for anything.