Add NCCL_ASYNC_ERROR_HANDLING to docs (#46856)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/46856
Add reference to NCCL_ASYNC_ERROR_HANDLING in the pytorch docs,
similar to how NCCL_BLOCKING_WAIT is curently described.
ghstack-source-id: 115186877
Test Plan: CI, verifying docs change
Reviewed By: jiayisuse
Differential Revision: D24541822
fbshipit-source-id: a0b3e843bc6392d2787a4bb270118f2dfda5f4ec
