[ONNX] Update scripting docs (#54634) (#54868)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/54868
* Updating docs for scripting
* Rebase
* Fix formatting
Test Plan: Imported from OSS
Reviewed By: nikithamalgifb
Differential Revision: D27408980
Pulled By: SplitInfinity
fbshipit-source-id: 2b176a5a746c1a2369be1940d84e6491a1ecd015
