Updates torch.clone documentation to be consistent with other functions (#43098)
Summary:
`torch.clone` exists but was undocumented, and the method incorrectly listed `memory_format` as a positional argument. This:
- documents `torch.clone`
- lists `memory_format` as a keyword-only argument
- wordsmiths the documentation
Pull Request resolved: https://github.com/pytorch/pytorch/pull/43098
Reviewed By: ngimel
Differential Revision: D23153397
Pulled By: mruberry
fbshipit-source-id: c2ea781cdcb8b5ad3f04987c2b3a2f1fe0eaf18b
