Update readme

[PimMeulensteen]

There was a TODO item for the exposed methods, this is fixed in this PR.

[JoBraNFI]

I think it would be nice to add a __all__ section to https://github.com/NetherlandsForensicInstitute/lr_module_scratch/blob/main/lrmodule/__init__.py as well to explicitly expose these functions and support autocompletion in editors like PyCharm.

__al__ = [
    'get_lr_system',
    'get_reference_data',
    'get_validation_experiment',
]