Add documentation for surrogate crystallizer (example) input and output requirements

[OOAmusat]

The surrogate crystallizer example/test needs more documentation around the linking of the surrogates and the crystallizer model.

A specific issue that needs to be explicitly addressed/mentioned is the importance of the order of the output variables provided to the crystallizer model, and how this needs to match the order of the variables in the surrogate output itself.

For example, if the outputs from the surrogate are in the order ["Calcite", "Halite"], then the surrogate addition to the crystallizer must also follow the same order in order to get the right/expected results, i.e.,

    surrogate_outputs = {
        "Calcite": {"flowsheet_var": m.fs.o1, "Solid": True},
        "Halite": {"flowsheet_var": m.fs.o2, "Solid": True},
    }

    add_crystallizer_model(
            m.fs.cryst,
            surrogate_inputs_with_bounds=surrogate_inputs,
            surrogate_outputs=surrogate_outputs,
        )