DOC: installer.sh: now telling the user that he needs to create a path if using option -p.
DOC: installer.sh: now telling the user that he needs to create a path if using option -p.

Former-commit-id: 2b6cfb0b38ad3c92432b931342dd424e14200866 [formerly b5b7c98becb2b110885fa1d3ba02cfd16ef5623e]
Former-commit-id: 6e8ec1273573550a93509c5af9bbb2eaf03956b6
Former-commit-id: 12822c6d47850e5f9b5984f97dbac40ff18e4e8a
neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox