[TP][EZ] Update doc for TP parallel style (#107819)
We need to update the doc for PairwiseParallel and SequenceParallel so that users don't get wrong impressions that these working for ``nn.Transformer``.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/107819
Approved by: https://github.com/awgu, https://github.com/wanchaol
