Add docs for c10::InferenceMode. (#57480)
Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/57480
Test Plan: Imported from OSS
Reviewed By: navahgar, pbelevich
Differential Revision: D28164070
Pulled By: ailzhang
fbshipit-source-id: a6b0658f3e65f76387095fbd8d66c762914d3bea
