更新 README.md

[skip ci]

README.md

@@ -20,7 +20,7 @@ docker logs gitea-runner-cache-server
 ```
 
 ```
-docker exec -it gitea-runner-cache-server rm -rf /runner-cache/cache/*
+docker exec -it gitea-runner-cache-server sh -c "rm -rf /runner-cache/cache/*"
 ```
 
 ## Gitea Runner