DOC: batch_processing: added start/end time
DOC: batch_processing: added start/end time

Former-commit-id: f9f0f1eb2c3f21bcb5b0cd3345611f1f934cea40
Former-commit-id: cc54f951bf9a8d7fb8bf91cb8b23eb74980505c2
3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox