docs: update deployment example

examples/docker-compose.scheduled.local.yaml

@@ -5,11 +5,12 @@ services:
     # release version instead of using `latest`.
     image: jkaninda/mysql-bkup
     container_name: mysql-bkup
-    command: backup --dbname database_name --mode scheduled --period "0 1 * * *"
+    command: backup --dbname database_name
     volumes:
       - ./backup:/backup
     environment:
       - DB_PORT=3306
       - DB_HOST=mysql
       - DB_USERNAME=userName
-      - DB_PASSWORD=${DB_PASSWORD}
+      - DB_PASSWORD=${DB_PASSWORD}
+      - BACKUP_CRON_EXPRESSION=0 1 * * * # Optional