[DOC] Add link from API page to sample_dataset.ipynb

the [api](https://chainladder-python.readthedocs.io/experimental/library/generated/chainladder.list_samples.html) page for list_samples() is pretty bare. would be good to point the reader to the full [listing](https://chainladder-python.readthedocs.io/experimental/library/sample_data.html). edit would be made in the docstring of the method