Added build note.

Author: killme2008

README.md

@@ -19,6 +19,20 @@ $ npm install avoscloud-sdk
 * [云代码开发指南](http://leancloud.cn/docs/cloud_code_guide.html)
 
 
+## Build
+
+We use [gulp](http://gulpjs.com/) to build the project.
+
+how to use:
+
+```sh
+npm install -g gulp 
+cd javascript-sdk
+npm install
+gulp pack        # = sh pack.sh
+gulp release    # = sh release (and use the VERSION number from av.js  automatically)
+```
+
 # 协议
 
 [MIT License](http://opensource.org/licenses/MIT)