Added example for SlidingWindowCmn transform (#2600)

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

Pull Request resolved: https://github.com/pytorch/audio/pull/2600

Reviewed By: mthrok

Differential Revision: D38395579

Pulled By: carolineechen

fbshipit-source-id: 44c5b7181789eedcaaa1d80149d5a1ab8de4c0ba

torchaudio/transforms/_transforms.py

@@ -1348,6 +1348,11 @@ class SlidingWindowCmn(torch.nn.Module):
         center (bool, optional): If true, use a window centered on the current frame
             (to the extent possible, modulo end effects). If false, window is to the left. (bool, default = false)
         norm_vars (bool, optional): If true, normalize variance to one. (bool, default = false)
+
+    Example
+        >>> waveform, sample_rate = torchaudio.load('test.wav', normalize=True)
+        >>> transform = transforms.SlidingWindowCmn(cmn_window=1000)
+        >>> cmn_waveform = transform(waveform)
     """
 
     def __init__(