Enhance reproducibility documentation (#33795)
Summary:
Improves explanation of non-determinism when running on GPUs. Adds info about `torch.nn.BCELoss` operating non-deterministically on GPUs.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/33795
Differential Revision: D20284880
Pulled By: ngimel
fbshipit-source-id: d543959636d261a80c234150304344b19a37ba5d
