message: update install doc
diff: @@ -72,6 +72,7 @@ behavior. See the table below.
  | MYSQL_USER | Yes | | User to connect to MySQL with |
  | MYSQL_PASSWORD | Yes | | Password to authenticate to MySQL |
  | MYSQL_DATABASE | Yes | | Database where the `mysql-schema` was applied |
  +| MYSQL_PORT | No | 3306 | The port of MySQL |
  | MYSQL_INSTANCE_CONNECTION_NAME | | | |
  | PUBLIC_URI | | http://localhost:8531 | |
  | PORT | | 8531 | Port to host the API on. |
  