update readme

README.md

@@ -54,7 +54,7 @@ pip install paddle-serving-server # CPU
 pip install paddle-serving-server-gpu # GPU
 ```
 
-You may need to use a domestic mirror source (in China, you can use the Tsinghua mirror source, add "-i https://pypi.tuna.tsinghua.edu.cn/simple" to pip command) to speed up the download.
+You may need to use a domestic mirror source (in China, you can use the Tsinghua mirror source, add `-i https://pypi.tuna.tsinghua.edu.cn/simple` to pip command) to speed up the download.
  
 Client package support Centos 7 and Ubuntu 18, or you can use HTTP service without install client.
 

README_CN.md

@@ -55,7 +55,7 @@ pip install paddle-serving-server # CPU
 pip install paddle-serving-server-gpu # GPU
 ```
 
-您可能需要使用国内镜像源（例如清华源, 在pip命令中添加"-i https://pypi.tuna.tsinghua.edu.cn/simple"）来加速下载。
+您可能需要使用国内镜像源（例如清华源, 在pip命令中添加`-i https://pypi.tuna.tsinghua.edu.cn/simple`）来加速下载。
 
 客户端安装包支持Centos 7和Ubuntu 18，或者您可以使用HTTP服务，这种情况下不需要安装客户端。