Add example for GriffinLim (#1671)

torchaudio/transforms.py

@@ -155,6 +155,12 @@ class GriffinLim(torch.nn.Module):
             Values near 1 can lead to faster convergence, but above 1 may not converge. (Default: ``0.99``)
         length (int, optional): Array length of the expected output. (Default: ``None``)
         rand_init (bool, optional): Initializes phase randomly if True and to zero otherwise. (Default: ``True``)
+
+    Example
+        >>> batch, freq, time = 2, 257, 100
+        >>> spectrogram = torch.randn(batch, freq, time)
+        >>> transform = transforms.GriffinLim(n_fft=512)
+        >>> waveform = transform(spectrogram)
     """
     __constants__ = ['n_fft', 'n_iter', 'win_length', 'hop_length', 'power',
                      'length', 'momentum', 'rand_init']