[ci skip]

add license badge

Author: longbai

README.md

@@ -1,5 +1,5 @@
 # Qiniu Objective-C SDK
-
+[![Software License](https://img.shields.io/badge/license-MIT-brightgreen.svg)](LICENSE.md)
 [![Build Status](https://travis-ci.org/qiniu/objc-sdk.svg?branch=master)](https://travis-ci.org/qiniu/objc-sdk)
 [![Latest Stable Version](https://badge.fury.io/co/Qiniu.png)](https://github.com/qiniu/objc-sdk/releases)