Add note to torch docs for sinh/cosh (#49413)
Summary:
Address https://github.com/pytorch/pytorch/issues/48641
Documents the behavior of sinh and cosh in the edge cases
```
>>> b = torch.full((15,), 89, dtype=torch.float32)
>>> torch.sinh(b)
tensor([2.2448e+38, 2.2448e+38, 2.2448e+38, 2.2448e+38, 2.2448e+38, 2.2448e+38,
2.2448e+38, 2.2448e+38, 2.2448e+38, 2.2448e+38, 2.2448e+38, 2.2448e+38,
2.2448e+38, 2.2448e+38, 2.2448e+38])
>>> b = torch.full((16,), 89, dtype=torch.float32)
>>> torch.sinh(b)
tensor([inf, inf, inf, inf, inf, inf, inf, inf, inf, inf, inf, inf, inf, inf, inf, inf])
>>> b = torch.full((17,), 89, dtype=torch.float32)
>>> torch.sinh(b)
tensor([ inf, inf, inf, inf, inf, inf,
inf, inf, inf, inf, inf, inf,
inf, inf, inf, inf, 2.2448e+38])
>>> b = torch.full((32,), 89, dtype=torch.float32)[::2]
>>> torch.sinh(b)
tensor([2.2448e+38, 2.2448e+38, 2.2448e+38, 2.2448e+38, 2.2448e+38, 2.2448e+38,
2.2448e+38, 2.2448e+38, 2.2448e+38, 2.2448e+38, 2.2448e+38, 2.2448e+38,
2.2448e+38, 2.2448e+38, 2.2448e+38, 2.2448e+38])
```
See https://sleef.org/purec.xhtml
Pull Request resolved: https://github.com/pytorch/pytorch/pull/49413
Reviewed By: ezyang
Differential Revision: D25587932
Pulled By: soulitzer
fbshipit-source-id: 6db75c45786f4b95f82459d0ce5efa37ec0774f0
