fix handler catalogue

Author: whiskeyfei

README.md

@@ -247,7 +247,10 @@ Welcome `Star` and `Fork`, your support is my greatest affirmation.
 1. [Android热更新实现原理](http://blog.csdn.net/lzyzsd/article/details/49843581#0-tsina-1-98317-397232819ff9a47a7b7e80a40613cfe1)
 2. [Android App 线上热修复方案](http://lirenlong.github.io/hotfix/)
 3. [Nuwa](https://github.com/jasonross/Nuwa)
-4. [Handler和他的小伙伴们](http://www.jianshu.com/p/e04698eaba88) 轻松理解Handler、message、looper
+
+### Handler
+
+1. [Handler和他的小伙伴们](http://www.jianshu.com/p/e04698eaba88) 轻松理解Handler、message、looper
 
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