Update SUMMARY.md

Author: Euler-37

src/SUMMARY.md

@@ -52,6 +52,7 @@
     - [指针](ch08-00-pointer.md)
     - [内存安全](ch08-01-memory.md)
     - [过程指针](ch08-02-procpointer.md)
+    - [指针的小技巧](ch08-03-pointertips.md)
 ## 附录
 
 - [mdBook参考](mdbook-cheat-sheet.md)