update readme: adding code-style

Author: xiaokai-wang

README.md

@@ -30,6 +30,7 @@ Table of Contents
 * [TODO](#todo)
 * [Compatibility](#compatibility)
 * [Installation](#installation)
+* [Code style](#code-style)
 * [Author](#author)
 * [Copyright and License](#copyright-and-license)
 * [See Also](#see-also)
@@ -387,6 +388,13 @@ make install
 
 [Back to TOC](#table-of-contents)
 
+Code style
+======
+
+Code style is mainly based on [style](http://tengine.taobao.org/book/appendix_a.html)
+
+[Back to TOC](#table-of-contents)
+
 Author
 ======