Update README.md

Author: tomleader

README.md

@@ -48,5 +48,14 @@ qcloud.cos.list('bucket', '/', 20, 'eListFileOnly');
 //获取指定目录下以'abc'开头的文件
 qcloud.cos.prefixSearch('bucket', '/firstDir/', 'abc', 20, 'eListFileOnly');
 
+//设置文件权限以及自定义header
+var headers = {
+        "Cache-Control": "no-cache",
+        "Content-Type" : "application/json",
+        "Content-Encoding" : "utf-8"
+    };
+    
+qcloud_cos.cos.updateFile('0001', '123/test_slice.dat', 'newattr', 'eWRPrivate', headers, function(ret) {console.log(ret)});
+
 ```