Update case1.md

docs/en_US/case/case1.md

@@ -5,7 +5,7 @@ Contributors:
 
 **Project**: [nezha_api_tgbot](https://github.com/spiritLHLS/nezha_api_tgbot) (Chinese)  
 
-**Mirror**: [nezha_api_tgbot](https://github.com/nezhahq/nezha_api_tgbot) (Chinese)  
+**Mirror backup, non-real-time update**: [nezha_api_tgbot](https://github.com/nezhahq/nezha_api_tgbot) (Chinese)  
 
 The bot can request server status information from the Dashboard through the API, and then send the information to the user.  
 You can build this bot to easily view the current status of a given server without opening the Dashboard.