Update CONTRIBUTING.rst
Update CONTRIBUTING.rst

Former-commit-id: 154c0efdb5b39e97a94d3b8fb173e919b6121a0c
neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox