Update README.md

Author: dp9u0

README.md

@@ -17,10 +17,6 @@
 * [整数运算](ch2/2.3.md)
 * [浮点数](ch2/2.4.md)
 * [字符编码](ch2/2.5.md)
-* Tips
-  * [一个关于dotfuscator_v5.9字符编码的Bug](https://github.com/dp9u0/Notebook-CSAPP/issues/6)
-  * [两个数不使用四则运算得出和(位运算)](https://github.com/dp9u0/Notebook-CSAPP/issues/5)
-  * [Unicode 编码分布](https://github.com/dp9u0/Notebook-CSAPP/issues/3)
 * Reference
   * [Unicode 11.0 Character Code Charts](https://www.unicode.org/charts/)
 
@@ -89,4 +85,4 @@
 
 * [异常分类](ch8/README.md#异常分类)
 * [进程](ch8/README.md#进程)
-* [信号](ch8/README.md#信号)
+* [信号](ch8/README.md#信号)