Update CONTRIBUTING.rst
Update CONTRIBUTING.rst

Former-commit-id: d6099da00abda0dc958f4d1649689ee5006a9075
neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox