Add example code for Pre-Built models

[tinaoberoi]

It would be useful to add code example for pre-built models.

Proposal (Can choose either one):

• Add Prebuilt code model example usage along with machine model example code in compilers section. https://bqskit.readthedocs.io/en/latest/source/autogen/bqskit.compiler.compile.html

• Add Example code usage next to the note about pre-built machine models. https://bqskit.readthedocs.io/en/latest/source/autogen/bqskit.compiler.MachineModel.html

Example:

model = Sycamore23Model
out_circuit = compile(circuit, model=model)

print("Gate Counts:", out_circuit.gate_counts)

print("Connectivity:", out_circuit.coupling_graph)

[edyounis]

This is a great suggestion! Thank you for this.