Update docs for torch.profiler.tensorboard_trace_handler (#51636)
Summary:
![image](https://user-images.githubusercontent.com/62738430/106856207-17f8c000-66f9-11eb-80c9-844f79de423e.png)
Pull Request resolved: https://github.com/pytorch/pytorch/pull/51636
Reviewed By: orionr
Differential Revision: D26246309
Pulled By: ilia-cher
fbshipit-source-id: 083868e9231727638238c5f5ca31e3566d5e2e7e