update readme

Author: code4craft

README.md

@@ -25,7 +25,7 @@ Netty是Java世界知名的网络应用框架。本系列文章是Netty的源码
 ### [1.概述](https://github.com/code4craft/netty-learning/blob/master/ch1-overview.md)
 ### [2.Netty中的buffer](https://github.com/code4craft/netty-learning/blob/master/ch2-buffer.md)
 ### [3.Channel与Pipeline](https://github.com/code4craft/netty-learning/blob/master/ch3-pipeline.md)
-### [4.Channel的生命周期](https://github.com/code4craft/netty-learning/blob/master/ch4-channel-lifecycle.md)
+### [4.Channel的生命周期](https://github.com/code4craft/netty-learning/blob/master/ch4-channel-lifecycle.md) *未完成*
 ### [5.Channel与Reactor模式](https://github.com/code4craft/netty-learning/blob/master/ch5-channel-nio.md) *未完成*
 ### [6.分门别类讲讲Handler](https://github.com/code4craft/netty-learning/blob/master/ch6-handler.md) *未完成*