Add missing words to torch.utils.checkpoint doc (#120196)
This PR adds a couple of missing words in the Checkpointing documentation, it doesn't have a specific issue number related to it.
Changes are:
- "backward." -> "backward propagation."
- "to be advanced than" -> "to be more advanced than"
Pull Request resolved: https://github.com/pytorch/pytorch/pull/120196
Approved by: https://github.com/soulitzer
