Add TORCH_SHOW_CPP_STACKTRACES to Contributing.md (#64052)
Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/64052
Reviewed By: ezyang
Differential Revision: D31107779
Pulled By: Chillee
fbshipit-source-id: 2ad8ad40cd48e54fe711863c3c74df884a2e2de7
