Merge pull request taizilongxu#41 from mathbugua/master

增加类方法和静态方法的参考资料

Author: taizilongxu

Readme.md

@@ -219,8 +219,9 @@ a=A()
 | a = A() | a.foo(x) | a.class_foo(x) | a.static_foo(x) |
 | A       | 不可用      | A.class_foo(x) | A.static_foo(x) |
 
-更多关于这个问题:http://stackoverflow.com/questions/136097/what-is-the-difference-between-staticmethod-and-classmethod-in-python
-
+更多关于这个问题:
+1. http://stackoverflow.com/questions/136097/what-is-the-difference-between-staticmethod-and-classmethod-in-python
+2. https://realpython.com/blog/python/instance-class-and-static-methods-demystified/
 ## 4 类变量和实例变量
 
 **类变量：**