[docs] Added compose to the cp command

Docker cannot detect the container if it's not using the compose file. Hence re-adding the compose for the copy command.

src/pages/selfhosted/selfhosted-guide.mdx

@@ -215,7 +215,7 @@ cp docker-compose.yml turnserver.conf management.json backup/
 To save the Management service databases, you need to stop the Management service and copy the files from the store directory using a docker compose command as follows:
 ```bash
 docker compose stop management
-docker cp -a management:/var/lib/netbird/ backup/
+docker compose cp -a management:/var/lib/netbird/ backup/
 docker compose start management
 ```