Document how BCELoss avoids infinite results (#33160)
Summary:
Issue https://github.com/pytorch/pytorch/issues/31453
Pull Request resolved: https://github.com/pytorch/pytorch/pull/33160
Differential Revision: D19835527
Pulled By: albanD
fbshipit-source-id: 82fd2dd46ffbc87e90ca8e100db411b6ff6bfe32
