Docs: Feedback for Programmatic Configuration

Hi, I have some feedback about [this page](https://github.com/hazelcast/imdg-docs/edit/v/4.1/docs/modules/configuration/pages/configuring-programmatically.adoc).

You should add the important information that the mapConfig has to be added to the main config using `Config::addMapConfig`. I know it's not a big deal, but would've saved me the few minutes to pull up the entire class definition for both `Config `& `MapConfig`