Add method add_hparams to API doc (#27344)
Summary:
Adds the method `add_hparams` to `torch.utils.tensorboard` API docs. Will want to have this in PyTorch 1.3 release.
cc sanekmelnikov lanpa natalialunova
Pull Request resolved: https://github.com/pytorch/pytorch/pull/27344
Differential Revision: D17753689
Pulled By: orionr
fbshipit-source-id: cc8636e0bdcf3f434444cd29471c62105491039d
