DOC: added usage + main
DOC: added usage + main

Former-commit-id: d66f837043bf788ef0ec1c2fe95b652f6ec09ed4 [formerly 3d257137d9c65f9b985e2c08c0fd3dc9ea11e98d]
Former-commit-id: 6e5b91bce43eb3aa0cef4c7923d195ef8eb17b14
Former-commit-id: 637569b975efbf9da62ee82f48c31633ed937251
neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox