add upgrade command into README

README.md

@@ -26,6 +26,7 @@
 # Installation
 ```shell
 $ pip install kwextraction -i http://dev.dp.sagacloud.cn:8082/repository/saga-pypi-group/simple --trusted-host dev.dp.sagacloud.cn
+$ pip install --upgrade kwextraction -i http://dev.dp.sagacloud.cn:8082/repository/saga-pypi-group/simple --trusted-host dev.dp.sagacloud.cn
 ```
 可定期自行更新设备信息文件
 ```shell