增加对 synchronized 关键字的总结

Author: Snailclimb

README.md

@@ -17,7 +17,7 @@
 
 -  ### Java 多线程
    - [多线程系列文章](https://github.com/Snailclimb/Java_Guide/blob/master/Java相关/多线程系列.md)
-
+   - [值得立马保存的 synchronized 关键字总结](https://github.com/Snailclimb/Java_Guide/blob/master/Java相关/synchronized.md)
 
 - ### Java IO 与 NIO
   - [Java IO 与 NIO系列文章](https://github.com/Snailclimb/Java_Guide/blob/master/Java相关/Java%20IO与NIO.md)