Added entry for torch.linalg.cond to linalg.rst (#48941)
Summary:
This PR makes documentation for `cond` available at https://pytorch.org/docs/master/linalg.html
I forgot to include this change in https://github.com/pytorch/pytorch/issues/45832.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/48941
Reviewed By: ngimel
Differential Revision: D25379244
Pulled By: mruberry
fbshipit-source-id: c8c0a0b8a05c17025d6c3cea405b2add369e2019
