Update 设计模式.md

Author: Snailclimb

docs/system-design/设计模式.md

@@ -71,7 +71,7 @@
 - **迭代器模式：**
 - **中介者模式：** <https://design-patterns.readthedocs.io/zh_CN/latest/behavioral_patterns/mediator.html>
 - **备忘录模式：**
-- **观察者模式：** <https://design-patterns.readthedocs.io/zh_CN/latest/behavioral_patterns/observer.html>
+- **观察者模式：** <https://design-patterns.readthedocs.io/zh_CN/latest/behavioral_patterns/observer.html>、<https://juejin.im/post/5c712ab56fb9a049a7127114>
 - **状态模式：**<https://design-patterns.readthedocs.io/zh_CN/latest/behavioral_patterns/state.html>
 - **策略模式：**<https://design-patterns.readthedocs.io/zh_CN/latest/behavioral_patterns/strategy.html>