Merge pull request #2 from renjinghai/patch-1

Fix a minor typo of user to use

Doing 互斥锁：synchronized.md

Little modify

Finish Java 内存模型.md

Java线程 modify bold format

Java线程 modify content

Java线程 add content

First finish Java 线程

First finish Java线程：使用篇.md

First finish Java线程-概念篇.md

add 极客时间 xmind

Create jcip-example-code project

modify readme

Add：RejectedExecutionHandler源码分析