add front end code (#27)

web/src/pages/404.jsx

@@ -0,0 +1,17 @@
+import { Button, Result } from 'antd';
+import React from 'react';
+import { history } from 'umi';
+
+const NoFoundPage = () => {
+  return (<Result
+    status="404"
+    title="404"
+    subTitle="页面未找到，请输入正确的地址。"
+    extra={< Button type="primary" onClick={() => history.push('/')}>
+      返回主页
+    </Button>}
+  />
+  )
+};
+
+export default NoFoundPage;