DOC: fixed issue #501
DOC: fixed issue #501

Former-commit-id: 42568430690838536772f94f18ac1b27ff4121ad
Former-commit-id: 6958b9553d92791fdd506772583cd23b6cd58714
3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox