def _add_neurodocker_header(specs):
    """Return Dockerfile comment that references Neurodocker."""
    return ("# Generated by Neurodocker v{}."
            "\n#"
            "\n# Thank you for using Neurodocker. If you discover any issues "
            "\n# or ways to improve this software, please submit an issue or "
            "\n# pull request on our GitHub repository:"
            "\n#     https://github.com/kaczmarj/neurodocker"
            "\n#"
            "\n# Timestamp: {}".format(specs['neurodocker_version'],
                                       specs['generation_timestamp']))