fixed comments referring fairscale master branch (#65531)
Summary:
replace comments referring fairscale master branch with main branch
Pull Request resolved: https://github.com/pytorch/pytorch/pull/65531
Test Plan:
buck build
cc pietern mrshenli pritamdamania87 zhaojuanmao satgera rohan-varma gqchen aazzolini osalpekar jiayisuse SciPioneer H-Huang gcramer23
Reviewed By: H-Huang, anj-s
Differential Revision: D31132552
Pulled By: tmarkstrum
fbshipit-source-id: d3ee8920ab5cccad99f640934c21e8eee022e9b9
