Pull request review etiquette

If you request changes on a pull request, this will block the pull request from landing. Basic etiquette in the PyTorch repository is that if you request changes, once the author updates their pull request to address your comments, you should re-review the pull request within 24 hours (after all, they are blocked on you! Try to keep them unblocked.) If you can't commit to this SLA, feel free to leave comments, but don't request changes (so that the pull request author knows it is at their discretion whether or not to address your comments or not.)