Improve example for torch.mode (#17069)
Summary:
This updates the example for `torch.mode` to show a case where there is a mode.
Also add a bit of a description to the explanation as well as being a bit more precise about "a" mode rather than "the" mode.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/17069
Differential Revision: D14078722
Pulled By: soumith
fbshipit-source-id: 837a238d53a9b8e868511acbdc258633975bea48
