[QDC Feedback] Add more info about layers

[javabster]

In one of the QDC challenges people were very confused about a specific example where the minimum number of layers was 2 not 3. this is a very nice small example to show how layering is somewhat subjective and I think it would be good to include this example in the one of the guides we have (maybe the noise learner one?). I noticed people struggling a bit with the general concept of layers so I think showing a concrete example like this in docs could help.

This is the notebook in question that had the layering example (ex3): https://github.com/qiskit-community/qdc-challenges-2024/blob/main/Day_3/QDC_Day_3_Track_A.ipynb