[torch/elastic] Update the rendezvous docs (#57973)
Summary:
This PR updates the rendezvous documentation for the Torch Distributed Elastic section of PyTorch docs.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/57973
Reviewed By: kiukchung
Differential Revision: D28331386
Pulled By: cbalioglu
fbshipit-source-id: 95dd32146222aaeff246bd3c3d2caf0036a9011b
