Slightly improve dataloader docs on when auto-batching is disabled (#23671)
Summary:
cc gchanan
Pull Request resolved: https://github.com/pytorch/pytorch/pull/23671
Differential Revision: D16604387
Pulled By: soumith
fbshipit-source-id: 0ebc120bcaa0f6fa09158b1d0459a72ab11a53d6
