[Gradient Compression] Update a warning in ddp_comm_hooks.rst (#55031)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/55031
It turns out that PowerSGD hooks can work on PyTorch native AMP package, but not Apex AMP package, which can somehow mutate gradients during the execution of communication hooks.
{F561544045}
ghstack-source-id: 125268206
Test Plan:
Used native amp backend for the same pytext model and worked:
f261564342
f261561664
Reviewed By: rohan-varma
Differential Revision: D27436484
fbshipit-source-id: 2b63eb683ce373f9da06d4d224ccc5f0a3016c88
