Merge pull request #68 from Authing/fix/update-readme

update readme

Author: erniu

README.md

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+**English** | [简体中文](./README.zh-CN.md)
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 The Authing SSO SDK provides developers with simple and easy-to-use functions to achieve the SSO effect on the web side. You can integrate with Authing by calling the SDK to achieve the SSO effect in the browser for your multiple business software.
 ## Install with NPM
 

README.zh-CN.md

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 </div>
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+**简体中文** | [English](./README.md)
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 Authing SSO SDK 为开发者提供了简单易用的函数来实现 Web 端的单点登录效果，你可以通过调用 SDK 与 Authing 完成集成，为你的多个业务软件实现浏览器内的单点登录效果。
 ## 使用 NPM 安装