REF: improved doc
REF: improved doc

Former-commit-id: ec0dbfe464f72c2a27fb4d541788bc6d6d462e22
Former-commit-id: 0fcc43a7307dec678ba1435264a5456d80f22877
3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox