fix typo in the docs of multiprocessing (#70448)
Summary:
Fix typo in the docs of multiprocessing.
cc pietern mrshenli pritamdamania87 zhaojuanmao satgera rohan-varma gqchen aazzolini osalpekar jiayisuse SciPioneer H-Huang
Pull Request resolved: https://github.com/pytorch/pytorch/pull/70448
Reviewed By: gchanan
Differential Revision: D33336962
Pulled By: H-Huang
fbshipit-source-id: 1235703b8ddc26c33dcbc34bd25ac36b11a18923
