Minor doc updates for S3 update procedure (#91978)
It would be good to make the s3_init_config.json instructions
more detailed (like step-by-step for how to run the custom build)
Signed-off-by: Edward Z. Yang <ezyang@fb.com>
Pull Request resolved: https://github.com/pytorch/pytorch/pull/91978
Approved by: https://github.com/malfet
