Computational notebooks help data scientists combine code and explanations, but often lack proper documentation. Themisto is a system that automatically generates different types of documentation for code, making it easier for data scientists to share their work. By using deep learning and online API documentation, Themisto reduces the time needed to write documentation and reminds users to document their code. In a study with data science practitioners, Themisto was found to improve satisfaction with computational notebooks by making documentation easier and more efficient.