Add a documentation about the usage of the Unity scripts for entity game objects

[coeing]

The question ocurred:

it seems like there are several classes that inherit from MonoBehaviour that are meant to be attached to gameobjects (EntityConfigurationBehaviour, EntityBehaviour, EntityGameObjectMap, etc.) It’s not clear to me what the proper way to connect Unity GOs to Slash component and the interactions, both ways, between the two.

[coeing]

If required the scripts have to be reworked, they were developed over time without a clear structure.

[coeing]

Cleanup of ECS scripts will be done in issue #45