readme文档修改，增加英文说明

README.md

@@ -38,10 +38,7 @@ Flutter上的一个日历控件，可以定制成自己想要的样子。
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-<img src="https://user-gold-cdn.xitu.io/2019/10/9/16db05f93d816799?w=828&h=1792&f=png&s=81540" width="280" height="620">
-</td>
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-<img src="https://user-gold-cdn.xitu.io/2019/10/9/16db05fa9949b0af?w=828&h=1792&f=png&s=124266" width="280" height="620">
+<img src="https://tva1.sinaimg.cn/large/006y8mN6ly1g8hjt66daxj30n01dsad5.jpg" width="280" height="620">
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 <img src="https://user-gold-cdn.xitu.io/2019/10/9/16db060ca77ecad2?w=828&h=1792&f=png&s=126261" width="280" height="620">

README_en.md

@@ -40,11 +40,9 @@ Calendar supports web Preview：[Click here for preview](https://lxd312569496.gi
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-<img src="https://user-gold-cdn.xitu.io/2019/10/9/16db05f93d816799?w=828&h=1792&f=png&s=81540" width="280" height="620">
-</td>
-<td>
-<img src="https://user-gold-cdn.xitu.io/2019/10/9/16db05fa9949b0af?w=828&h=1792&f=png&s=124266" width="280" height="620">
+<img src="https://tva1.sinaimg.cn/large/006y8mN6ly1g8hjt66daxj30n01dsad5.jpg" width="280" height="620">
 </td>
+
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 <img src="https://user-gold-cdn.xitu.io/2019/10/9/16db060ca77ecad2?w=828&h=1792&f=png&s=126261" width="280" height="620">
 </td>