update docker mysql import info

README.md

@@ -33,7 +33,7 @@ docker-compose exec --user www-data app php occ
 ## Datenbank
 MySQL import
 ```
-docker exec -i nextcloud-db mysql -uroot -p nextcloud < SQLFILE.sql
+docker exec -i nextcloud-db mysql -u<MYSQL_USER> -p<MYSQL_PASSWORD> nextcloud < SQLFILE.sql
 ```
 MySQL Dump
 ```