DOC: added description of the program
DOC: added description of the program

Former-commit-id: a6285fd9530e3e9e3886b718cda47c9d2d82a140
Former-commit-id: 5acf84d2a24bf973945a60368401c318803c3bee
3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox