Update tutorials to include super().__init__() when subclassing mesa.model

[davidbailey]

Describe the bug
The tutorials (e.g. https://mesa.readthedocs.io/en/stable/tutorials/intro_tutorial.html) instruct users to subclass mesa.model. However they do not say to include super().init(). In https://github.com/projectmesa/mesa/blob/main/mesa/model.py#L62-L77 it states you should "Always start with super().init() to initialize the model object properly."

Expected behavior
The documentation should tell users how to properly use the mesa.model class. The examples should include super().init() when subclassing mesa.model

To Reproduce
Not applicable.

Additional context
None.

[rht]

Closed via #2025.