Usage of `TimeStretch` is incorrect in documentation.

[tky823]

🐛 Describe the bug

In an example of https://pytorch.org/audio/stable/transforms.html, TimeStretch takes arguments as follows:

TimeStretch(stretch_factor, fixed_rate=True)

This usage is incorrect.

According to https://pytorch.org/audio/stable/generated/torchaudio.transforms.TimeStretch.html, this class takes the arguments of hop_length, n_freq, and fixed_rate.

Versions

I've checked this for torchaudio=2.0.1, but we can see the same issue for the older versions.