Update psi4_waveform_generator.py add a couple commetns

bilby/gw/psi4_waveform_generator.py

@@ -67,8 +67,10 @@ class Psi4_WaveformGenerator(WaveformGenerator):
         phase = 2 * np.pi * self.frequency_array / self.sampling_frequency
 
         self.correction_factor = \
+            # (A5) in the draft
             (1 - np.cos(phase)) / (0.5 * phase * phase) \
                 if self.is_psi4_model else \
+            # (A4) in the draft
             2 * self.sampling_frequency * self.sampling_frequency * (np.cos(phase) - 1)
 
         self._cache = dict(parameters=None, FD_waveform=None, TD_waveform=None)