Improve documentation of parity prefactor

[redeboer]

It's not well documented how the parity_prefactor is imported when building an amplitude.

Example

import qrules
import ampform
result_helicity = qrules.generate_transitions(
    initial_state=("J/psi(1S)", [-1, +1]),
    final_state=["K0", "p~", "Sigma+"],
    allowed_intermediate_particles=["N(1880)","Sigma(1750)"],
    formalism="helicity",
    max_angular_momentum=10,
    max_spin_magnitude=10,
    allowed_interaction_types="strong",
    particle_db=pdg,
)
model_builder_helicity = ampform.get_builder(result_helicity)

model_builder_helicity.align_spin=False
model_helicity = model_builder_helicity.formulate()
amplitude=list(model_helicity.amplitudes.keys())[-1]
display(amplitude)
model_helicity.amplitudes[amplitude]

[Leongrim]

The factor 1.0 is affected by whether helicities are inserted into the coefficient names.

import ampform
result_helicity = qrules.generate_transitions(
    initial_state=("J/psi(1S)", [-1, +1]),
    final_state=["K0", "p~", "Sigma+"],
    allowed_intermediate_particles=["N(1880)"],
    formalism="helicity",
    max_angular_momentum=10,
    max_spin_magnitude=10,
    allowed_interaction_types="strong",
    particle_db=pdg,
)
model_builder_helicity = ampform.get_builder(result_helicity)

model_builder_helicity.naming.insert_parent_helicities = True

model_builder_helicity.align_spin=False
model_helicity = model_builder_helicity.formulate()
amplitude=list(model_helicity.amplitudes.keys())[-1]
display(amplitude)
model_helicity.amplitudes[amplitude]