update README.md

Author: csuldw

README.md

@@ -4,6 +4,9 @@
 
 - Logistic Regression (二分类):  [source](https://github.com/csuldw/MachineLearning/tree/master/Logistic%20Regression) 。包含数据集和源码。
 
+- Decision Tree: 决策树，[源代码](https://github.com/csuldw/MachineLearning/tree/master/DecisionTree).
+
+
 - ROC: 用于绘制ROC曲线，[源代码](https://github.com/csuldw/MachineLearning/tree/master/ROC).
 
 # Contributor