Added example for LFCC transform (#2640)

Summary:
Added example for LFCC transform as mentioned in issue https://github.com/pytorch/audio/issues/1564.

Pull Request resolved: https://github.com/pytorch/audio/pull/2640

Reviewed By: carolineechen

Differential Revision: D38908975

Pulled By: nateanl

fbshipit-source-id: ffdd994390db7f27556b011a8050a65eef9cd09d

torchaudio/transforms/_transforms.py

@@ -757,6 +757,14 @@ class LFCC(torch.nn.Module):
         log_lf (bool, optional): whether to use log-lf spectrograms instead of db-scaled. (Default: ``False``)
         speckwargs (dict or None, optional): arguments for Spectrogram. (Default: ``None``)
 
+    Example
+        >>> waveform, sample_rate = torchaudio.load("test.wav", normalize=True)
+        >>> transform = transforms.LFCC(
+        >>>     sample_rate=sample_rate,
+        >>>     n_lfcc=13,
+        >>>     speckwargs={"n_fft": 400, "hop_length": 160, "center": False},
+        >>> )
+        >>> lfcc = transform(waveform)
 
     See also:
         :py:func:`torchaudio.functional.linear_fbanks` - The function used to