Merge pull request #2269 from chrisxu2016/gh-pages

add 404 pages

404.md

+---
+title: 404
+layout: page
+permalink: /404.html 
+---
+
+<script language="JavaScript"> function myrefresh(){window.location="/";}setTimeout('myrefresh()',5000);</script>
+
+## Error 404. Nothing was found :(   
+
+This is not the correct link you are looking for.
+
+Please go to [homepage](/) or contact us: paddle-dev@baidu.com
+
+
+## The page will redirect to the homepage after 5 seconds.....
\ No newline at end of file