Update determinism documentation (#41692)
Summary:
Add user-facing documentation for set_deterministic
Also update grammar and readability in Reproducibility page
Issue https://github.com/pytorch/pytorch/issues/15359
Pull Request resolved: https://github.com/pytorch/pytorch/pull/41692
Reviewed By: ailzhang
Differential Revision: D23433061
Pulled By: mruberry
fbshipit-source-id: 4c4552950803c2aaf80f7bb4792d2095706d07cf
