Improve the doc and test of logical_xor (#28031)
Summary:
Following up https://github.com/pytorch/pytorch/issues/27248. per suggestion by gchanan
Pull Request resolved: https://github.com/pytorch/pytorch/pull/28031
Differential Revision: D17962226
Pulled By: gchanan
fbshipit-source-id: 788e4e1fc78b1cfc7915aedaa10c8656b19edc4d
