修改 README

JamesZBL · JamesZBL · commit 6730cebed564 · 2017-11-16T19:05:19.000+08:00
diff --git a/README.md b/README.md
@@ -31,6 +31,8 @@
 
 [Prototype (原型模式)](https://github.com/JamesZBL/java_design_patterns/tree/master/prototype)
 
+[Singleton (单例模式)](https://github.com/JamesZBL/java_design_patterns/tree/master/singleton)
+
 ### 结构型模式
 
 [Adapter (适配器)](https://github.com/JamesZBL/java_design_patterns/tree/master/adapter)
