doc fix for max method: a warning about different behaviour on CPU and GPU (#31115)
Summary:
Fixes [30708](https://github.com/pytorch/pytorch/issues/30708),
Adds warning regarding different behaviour of the method depending on device type.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/31115
Differential Revision: D18937365
Pulled By: zou3519
fbshipit-source-id: 7c731dd80f8b371de08d7fdfcc2196be15a593e1
