Updates to serialization.md (#31372)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/31372
Keeping it current with the latest changes.
Test Plan: Imported from OSS
Differential Revision: D19145986
Pulled By: suo
fbshipit-source-id: 88122e66fa87a354ef8e87faffe58551074e3f03
