add better logo (#166)

README.cn.md

 <p align="center">
-  <img src="https://github.com/daming-lu/large_files/blob/master/visualdl-readme.png" width="60%" />
+  <img src="./docs/images/vs-logo.png" width="60%" />
 </p>
 
-# VisualDL (Visualize the Deep Learning)
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 ## 介绍
 VisualDL是一个面向深度学习任务设计的可视化工具，包含了scalar、参数分布、模型结构、图像可视化等功能，项目正处于高速迭代中，新的组件会不断加入。
 

README.md

 <p align="center">
-  <img src="https://github.com/daming-lu/large_files/blob/master/visualdl-readme.png" width="60%" />
+  <img src="./docs/images/vs-logo.png" width="60%" />
 </p>
 
-# VisualDL (Visualize the Deep Learning)
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 ## Introduction
 VisualDL is a deep learning visualization tool that can help design deep learning jobs.
 It includes features such as scalar, parameter distribution, model structure and image visualization.