[seq2seq] document the caveat of leaky native amp (#8930)
[seq2seq] document the caveat of leaky native amp (#8930)

* document the caveat of leaky native amp

* Update examples/seq2seq/README.md

Co-authored-by: Sylvain Gugger <222c4d44cc8ec39802c192ed0aa3f97cdb77ff4e@users.noreply.github.com>

Co-authored-by: Sylvain Gugger <222c4d44cc8ec39802c192ed0aa3f97cdb77ff4e@users.noreply.github.com>
huggingface/pytorch-transformers,huggingface/transformers,huggingface/transformers,huggingface/transformers,huggingface/transformers