[torchbind] Add more comprehensive docscrings (#34906)
Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/34906
Test Plan: Imported from OSS
Differential Revision: D20496221
Pulled By: jamesr66a
fbshipit-source-id: 3863ec77324564f6f0f1c54b0cbd6c29d12f3c74
