update the doc ,add the description about the retry mechanism feature

Author: lemon

README.md

@@ -4,6 +4,8 @@
 
 # UPDATES
 
+* 2017/04/09 adding the retry mechanism of injecting bridge
+
 * 2017/04/08  invoke Java synchornized from Javascript is now enable in `feature/sync`
 
   Now the `BridgeHandler` has two function to be invoked from JavaScript.If the JavaScirpt invoke Java with a callback function,the Java method will be invoked Synchronizlly ,otherwise the Java method will be invoked asynchronous.
@@ -13,6 +15,16 @@
 
 # FEATURES
 
+#### ✔️Inject Bridge with retry mechanism 
+
+Now when EasyBridge try to inject a comunication bridge into the page,it will retry at most five times to make sure that the bridge is injected successfully .It works as below:
+
+1. `EasyBridgeWebView` will register a handler name "injectFinished" default
+2. when the bridge injected finish,it will invoke the handler in step one, and set the injected status to be true
+3. When injecting a bridge ,it will start a task `InjectBridgeTask`,it will try to inject the bridge every 300ms at most 5 times,if the injected status  is false 
+
+**because of the single thread mechanism in JavaScrpt,we will make sure that the bridge will not be injected twice in the same page** 
+
 #### ✔️ Register Handler with APT
 
 Now you can register Handlers using the APT tech.Follow the steps:
@@ -92,7 +104,17 @@ You can set your policy according to the current page's url and the parameters y
 
 # <a name="README_CN">功能</a>
 
-#### ✔️ 使用apt技术注册handler
+#### ✔️ 注入jsbridge添加重试机制
+
+现在当我们往页面中注入bridge的时候，具备了重试机制。EasyBridge最多会尝试5次重试，尽可能的确保bridge被注入成功。重试机制的工作流程如下：
+
+1. 当我们初始化`EasyBridgeWebView`的时候，它会默认的注册一个名称为`injectFinished`的handler，用以监听bridge注入成功，并设置标志值
+2. 在bridge注入成功之后，会调用上面注册的那个handler，通知native，bridge已经注入成功了；
+3. 在注入bridge的时候，会启动一个`InjectBridgeTask`的任务，在注入成功的标志状态值`isInjected`为false的情况下，它会每隔300ms发起一次注入bridge的操作（最多重试5次）
+
+**因为JavaScript是单线程的，所以我们能确保同一个页面不会出现重复注入bridge的情况**
+
+####  使用apt技术注册handler
 
 支持使用apt技术，完成注册handler的功能，步骤如下：