Writing docs.

@@ -2,7 +2,7 @@
 
 <div align="center">  
 
-<img src="https://ws4.sinaimg.cn/large/006tNbRwly1fylahz0rrgj30p008ca9x.jpg"  /> 
+<img src="https://i.loli.net/2020/02/21/rfOGvKlTcHCmM92.png"  /> 
 <br/>
 
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