change readme

README.md

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-# <center style='color: #39c5bb'>Mirai</center>
+<div align="center">
+  <a href="https://mamoe.net" target="_blank">
+    <img width="160" src="http://img.mamoe.net/2020/02/16/a759783b42f72.png" alt="logo">
+  </a>
+  <h1 id="koishi"><a style="color: #39C5BB">Mirai</a></h1>
 
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 [![Download](https://api.bintray.com/packages/him188moe/mirai/mirai-core/images/download.svg)](https://bintray.com/him188moe/mirai/mirai-core/)  
+
+</div>
+
 **[English](README-eng.md)**  
 
 多平台 **QQ Android 和 TimPC** 协议支持库与高效率的机器人框架.