Update README.md

Author: kinosang

README.md

@@ -1,7 +1,7 @@
-Omnipay-Wechat
+Omnipay-WeChat
 ===
 
-**Wechat Payment driver for the Omnipay PHP payment processing library**
+**WeChat Payment driver for the Omnipay PHP payment processing library**
 
 [![Build Status](https://img.shields.io/travis/labs7in0/omnipay-wechat.svg)](https://travis-ci.org/labs7in0/omnipay-wechat)
 [![Packagist Status](https://img.shields.io/packagist/v/labs7in0/omnipay-wechat.svg)](https://packagist.org/packages/labs7in0/omnipay-wechat)
@@ -34,6 +34,12 @@ The following gateways are provided by this package:
 For general usage instructions, please see the main [Omnipay](https://github.com/thephpleague/omnipay)
 repository.
 
+WeChat JSAPI require OAuth openid to submit a new order, use `$WeChat_Express->getAuthCode($callback)` to get an url for WeChat OAuth and `$WeChat_Express-->getOpenid($code)` in callback page to get openid.
+
+p.s. the url for WeChat OAuth must be opened in WeChat In-App broswer, you can use `strpos($_SERVER['HTTP_USER_AGENT'], 'MicroMessenger') === false` to check if the page were not opened in it, and generate a QR code for user.
+
+All methods for WeChat OAuth will be removed in next stable version and I'll publish a WeChat MP library package for composer.
+
 ## Donate us
 
 [Donate us](https://7in0.me/#donate)