add requirement for indentation

README.md

@@ -99,7 +99,7 @@ brpc welcomes contributions, especially those on adapting different platforms an
 
 Make sure the code meets following requirements before submitting your PR:
 
-- Conforms to [google C++ coding style](https://google.github.io/styleguide/cppguide.html) and set 1 tab to 4 spaces.
+- The code conforms to [google C++ coding style](https://google.github.io/styleguide/cppguide.html) and is indented by 4 spaces.
 - The code appears where it should be. For example the code to support an extra protocol should not be put in general classes like server.cpp, channel.cpp, while a general modification would better not be hidden inside a very specific protocol.
 - Has unittests.
 

README_cn.md

@@ -100,7 +100,7 @@ brpc欢迎贡献代码，特别是对不同平台，协议的扩展代码。
 
 提交PR前请确认你的代码符合如下要求：
 
-* 符合[google C++代码规范](https://google.github.io/styleguide/cppguide.html), 并把1个tab设置为4个空格。
+* 符合[google C++代码规范](https://google.github.io/styleguide/cppguide.html), 且一次缩进为4个空格。
 * 代码出现的位置和其定位相符。比如对于某特定协议的扩展代码不该出现在server.cpp, channel.cpp这些较为通用的类中，而一些非常通用的改动也不该深藏在某个特定协议的cpp中。
 * 有对应的单测代码。