GitLab

Summary:
Added example for [Vol transform](https://pytorch.org/audio/stable/transforms.html#torchaudio.transforms.Vol) as mentioned in this issue https://github.com/pytorch/audio/issues/1564.

Also made a minor edit to the docstring for `class Vol` to fix a grammar typo and use more common verbiage.

Pull Request resolved: https://github.com/pytorch/audio/pull/2597

Reviewed By: nateanl, mthrok

Differential Revision: D38316433

Pulled By: carolineechen

fbshipit-source-id: 0be8fc505800a59acdab843813767acfdeac8243