Update PyTorch/Python version tip (#12402)
PyTorch 2.6.0 supports Python 3.13, and publishes wheels for it. Update
the tip to reflect this.
## Summary
Clarify docs.
## Test Plan
Look for "cp313" at the following URLs:
- [x] https://download.pytorch.org/whl/cu124/torch/
- [x] https://download.pytorch.org/whl/torch/
