Add note about TCP init in RPC tests to contributing doc. (#50861)
Summary:
We added this option in https://github.com/pytorch/pytorch/pull/48248, but it would be good to document it somewhere as well, hence adding it to this contributing doc.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/50861
Reviewed By: mrshenli
Differential Revision: D26014505
Pulled By: rohan-varma
fbshipit-source-id: c1321679f01dd52038131ff571362ad36884510a
