Update docstring for load_topostats.py

[ns-rse]

The Returns and Example
for load_toposats.py do not reflect what is returned by the function which is image, pixel_to_nm_scaling, data.

I.e. the data is not included.

This looks like a change in the .topostats file specification and the way things are structured perhaps and has had a knock-on effect when working on Expand usage of AFMReader for all file formats.... The changes are in refactor(io): Load .spm with AFMReader but as of writing the tests/test_run_modules.py::test_run_topostats_process_all() and tests/test_run_modules.py::test_run_topostats_process_debug() are failing because process_scan() is now being passed a np.ndarray() rather than the expected dictionary.

What should be returned, image, pixel_to_nm_scaling or should it it include data? 🤔