resolve changkun#16: fixing typo error

Author: changkun

README-en-us.md

@@ -4,7 +4,7 @@
 
 ![](https://img.shields.io/badge/version-v2-green.svg) ![](https://img.shields.io/badge/language-English-blue.svg) [![](https://img.shields.io/badge/$-donate-ff69b4.svg)](./assets/donate.md) [![](https://img.shields.io/badge/chat-community-667ed5.svg)](./assets/community.md) 
 
-> This book is adapting to C++17
+> This book is adapting to C++17 and translating to English.
 
 ## Languages
 
@@ -45,9 +45,9 @@ There are few exercises At the end of each chapter of the book. It is for testin
 
 ## Acknowledgements
 
-This book is originally written in Chinese, and the author's time, skills and languages are limited. If readers find any mistakes of the book or any language improvements, please feel free to open an [issue](https://github.com/changkun/modern-cpp-tutorial/issues). The author would like to appreciate all of the contributors of this book for discovering mistakes:
+This book is originally written in Chinese.
 
-[recolic](https://www.gitbook.com/@recolic), [sinomiko](https://www.gitbook.com/@sinomiko), [jackwish](https://www.gitbook.com/@jackwish), [asmwarrior](https://www.gitbook.com/@asmwarrior), [garicc](https://www.gitbook.com/@ihpy), [jiangwenhan](https://www.gitbook.com/@jiangwenhan), [liangx8](https://www.gitbook.com/@liangx8), [slivermeteor](https://github.com/slivermeteor), [inkedawn](https://github.com/inkedawn), [zhaoyao73](https://github.com/zhaoyao73), [sundy-li](https://github.com/sundy-li), [dontpanic92](https://github.com/dontpanic92)
+The author has limited time and language skills. If readers find any mistakes of the book or any language improvements, please feel free to open an [issue](https://github.com/changkun/modern-cpp-tutorial/issues).
 
 ## Licenses
 

README.md

@@ -10,7 +10,7 @@
 
 ## 语言
 
-- 🇨🇳 [简体中文](./README.md)
+- 🇨🇳 简体中文
 - 🇬🇧 [English](./README-en-us.md)
 
 ## 本书目的
@@ -46,7 +46,7 @@
 
 笔者时间和水平有限，如果读者发现书中内容的错误，欢迎提 [issue](https://github.com/changkun/cpp1x-tutorial/issues)。并感谢以下读者指出本书中出现的错误：
 
-[Recolic Keghart](https://www.gitbook.com/@recolic), [sinomiko](https://www.gitbook.com/@sinomiko), [Wang Zhenhua](https://www.gitbook.com/@jackwish), [asm warrior](https://www.gitbook.com/@asmwarrior), [garicc](https://www.gitbook.com/@ihpy), [Wenhan Jiang](https://www.gitbook.com/@jiangwenhan), [liang xiao](https://www.gitbook.com/@liangx8), [slivermeteor](https://github.com/slivermeteor), [inkedawn](https://github.com/inkedawn), [zhaoyao73](https://github.com/zhaoyao73), [sundy-li](https://github.com/sundy-li), [dontpanic92](https://github.com/dontpanic92)
+[recolic](https://www.gitbook.com/@recolic), [sinomiko](https://www.gitbook.com/@sinomiko), [jackwish](https://www.gitbook.com/@jackwish), [asmwarrior](https://www.gitbook.com/@asmwarrior), [garicc](https://www.gitbook.com/@ihpy), [jiangwenhan](https://www.gitbook.com/@jiangwenhan), [liangx8](https://www.gitbook.com/@liangx8), [slivermeteor](https://github.com/slivermeteor), [inkedawn](https://github.com/inkedawn), [zhaoyao73](https://github.com/zhaoyao73), [sundy-li](https://github.com/sundy-li), [dontpanic92](https://github.com/dontpanic92), [axionl](https://github.com/axionl), [Rholais](https://github.com/changkun/modern-cpp-tutorial/commits?author=Rholais) [MikuGhoul](https://github.com/MikuGhoul), [coderall](https://github.com/coderall)
 
 ## 许可
 

book/zh-cn/02-usability.md

@@ -114,7 +114,7 @@ int main() {
 > 注意，现在大部分编译器其实都带有自身编译优化，很多非法行为在编译器优化的加持下会变得合法，若需重现编译报错的现象需要使用老版本的编译器。
 
 
-C++11 提供了 `constexpr` 让用户显式的声明函数或对象构造函数在编译器会成为常数，这个关键字明确的告诉编译器应该去验证 `len_foo` 在编译器就应该是一个常数。
+C++11 提供了 `constexpr` 让用户显式的声明函数或对象构造函数在编译器会成为常数，这个关键字明确的告诉编译器应该去验证 `len_foo` 在编译期就应该是一个常数。
 
 此外，`constexpr` 的函数可以使用递归：