Update CONTRIBUTING.rst
Update CONTRIBUTING.rst

Former-commit-id: 38ddccbfd99d8de8733990ed979edf0e1d6b4574
neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox