[dist_optim] update the doc of DistributedOptimizer (#51314)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/51314
updating the doc of DistributedOptimizer to include TorchScript enablement information
Test Plan: Imported from OSS
Reviewed By: pbelevich
Differential Revision: D26156032
Pulled By: wanchaol
fbshipit-source-id: 1f3841f55918a5c2ed531cf6aeeb3f6e3a09a6a8
