[Doc][NVTX] Add documentation for nvtx.range (#121699)
The context manager `torch.cuda.nvtx.range` has been around for about 4 years (see #42925). Unfortunately, it was never documented and as a consequence users are just unaware of it (see #121663).
Pull Request resolved: https://github.com/pytorch/pytorch/pull/121699
Approved by: https://github.com/janeyx99
