Added example for MelScale transform (#2616)

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

Pull Request resolved: https://github.com/pytorch/audio/pull/2616

Reviewed By: carolineechen

Differential Revision: D38743145

Pulled By: nateanl

fbshipit-source-id: e24ca92f5317a0ea5a141418bf084b12cfb22486

torchaudio/transforms/_transforms.py

@@ -355,6 +355,13 @@ class MelScale(torch.nn.Module):
             (area normalization). (Default: ``None``)
         mel_scale (str, optional): Scale to use: ``htk`` or ``slaney``. (Default: ``htk``)
 
+    Example
+        >>> waveform, sample_rate = torchaudio.load("test.wav", normalize=True)
+        >>> spectrogram_transform = transforms.Spectrogram(n_fft=1024)
+        >>> spectrogram = spectrogram_transform(waveform)
+        >>> melscale_transform = transforms.MelScale(sample_rate=sample_rate, n_stft=1024 // 2 + 1)
+        >>> melscale_spectrogram = melscale_transform(spectrogram)
+
     See also:
         :py:func:`torchaudio.functional.melscale_fbanks` - The function used to
         generate the filter banks.