Update CONTRIBUTING.md
Update CONTRIBUTING.md

Co-Authored-By: Elizabeth DuPre <b5f1d46dee7a6dc3f899f145309a094f51075ed9@cornell.edu>
poldracklab/fmriprep,poldracklab/fmriprep,oesteban/fmriprep,oesteban/fmriprep,poldracklab/fmriprep,poldracklab/preprocessing-workflow,poldracklab/preprocessing-workflow,oesteban/fmriprep