DOC Improves input and target docstring for loss functions (#60553)
Summary:
Fixes https://github.com/pytorch/pytorch/issues/56581
Pull Request resolved: https://github.com/pytorch/pytorch/pull/60553
Reviewed By: VitalyFedyunin
Differential Revision: D29343797
Pulled By: jbschlosser
fbshipit-source-id: cafc29d60a204a21deff56dd4900157d2adbd91e
