message: Update documentation.
  Add `MARIADB_MAX_ALLOWED_PACKET` to the list of environment variables.
diff: @@ -30,6 +30,7 @@ Environment variables defined in MariaDB base image
  | `MARIADB_ROOT_PASSWORD` | Lag00n | MariaDB root user's password |
  | `MARIADB_CHARSET` | utf8mb4 | Set the server charset |
  | `MARIADB_COLLATION` | utf8mb4_bin | Set server collation |
  +| `MARIADB_MAX_ALLOWED_PACKET` | 64M | Set the max_allowed_packet size |
  | `MARIADB_INNODB_BUFFER_POOL_SIZE` | 256M | Set the MariaDB InnoDB Buffer Pool Size |
  | `MARIADB_INNODB_BUFFER_POOL_INSTANCES` | 1 | Number of InnoDB Buffer Pool instances |
  | `MARIADB_INNODB_LOG_FILE_SIZE` | 64M | Size of InnoDB log file |
  