CONTRIBUTING.md: add instructions on how to remote desktop into Windows CI (#50841)
Summary:
Adds a link to existing instructions in CONTRIBUTING.md, so those instructions are more visible to contributors.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/50841
Reviewed By: samestep
Differential Revision: D25983089
Pulled By: janeyx99
fbshipit-source-id: 0b777ec760765153c607515ab09441dd0cfddf3c
