Add document of function torch.as_strided (#22842)
Summary:
Documentation of `torch.as_strided` and `Tensor.as_strided` is missing. As mentioned in https://github.com/pytorch/pytorch/issues/9886
Pull Request resolved: https://github.com/pytorch/pytorch/pull/22842
Differential Revision: D16254106
Pulled By: soumith
fbshipit-source-id: dee142483fb9ef7bea84bd44a970b6eccdcdc471
