Enhance MacOS instructions for Qiskit C API to clarify Python dylib requirement

[cometta]

fix for #3934

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One or more of the following people are relevant to this code:

• @abbycross
• @beckykd
• @Cryoris

[abbycross]

Update: @Cryoris is checking on a Linux environment

[Cryoris]

@cometta thanks for proposing the updated docs. I think we should be clear here that we generally depend on the Python library on any platform, and if the Python libraries are not included in the runtime library path, they have to be added manually. On Linux this is less of a problem compared to Mac, I think, since the Python libs are there per default, but it would be good to be explicit nevertheless.