Add suggestion of datalad config

[Remi-Gau]

see https://docs.openneuro.org/git#repository-conventions

* annex.backend=SHA256E
**/.git* annex.largefiles=nothing
logs/* annex.largefiles=nothing
*.json annex.largefiles=largerthan=1mb
*.tsv annex.largefiles=largerthan=1mb
*.tsv.gz annex.largefiles=largerthan=1mb
dataset_description.json annex.largefiles=nothing
.bidsignore annex.largefiles=nothing
CHANGES annex.largefiles=nothing
README* annex.largefiles=nothing
LICENSE annex.largefiles=nothing