Add comment about running C++ executable lint locally (#46698)
Summary:
I got confused while locally running some of the `quick-checks` lints (still confused by `.jenkins/run-shellcheck.sh` but that's a separate matter) so I'm adding a comment to the "Ensure C++ source files are not executable" step in case someone in the future tries it and gets confused like I did.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/46698
Reviewed By: walterddr
Differential Revision: D24470718
Pulled By: samestep
fbshipit-source-id: baacd8f414aa41b9b7b7aac765d938f21085eac5
