add data sharing questions

docs/data.md

docs/data/bids.md

docs/data/can-i-deident.md

docs/data/can-i-ethics.md

docs/data/can-i-gov.md

docs/data/can-i-meta.md

docs/data/can-i-reuse.md

docs/data/can-i.md

docs/data/docker.md

docs/data/how.md

docs/data/opdc.md

docs/data/python.md

docs/data/when.md

docs/data/why.md

docs/data/xnat-tools.md

docs/protocols/protocols_guide_external.md