[Feat] Clarify documentation of grass.jupyter.Session finish procedures

[wenzeslaus]

Is your feature request related to a problem?

grass.jupyter.Session automatically closes the session, but the documentation and examples are not clear enough that user typically does not do anything because finish method is still there too.

Describe the solution you'd like

First, causal reading of the documentation should leave reader with the (correct) impression that the documentation is not need.

Additional context

Discussion with a good overview of what is in the documentation now:

veroandreo/foss4g2022_grass4rs#3