Add documentation for methods of data access with cdippy at to [this page](https://github.com/cdipsw/CDIPpy/blob/main/docs/user_guide/data_access.md). See: - [current documentation](https://cdipsw.github.io/CDIPpy/user_guide/data_access/) - [contributing documentation](https://cdipsw.github.io/CDIPpy/dev_guide/contribute/#documenting)
