Test the package with example data

[bobleesj]

Problem

The current package does not provide example data while the main app below requires input_directory

def main():
    args = create_parser()
    if args.input_directory is None:
        args.input_directory = Path.cwd()
    grid, input_data = load_input_signals(args.input_directory)

Proposed solution

We can attempt to use test data nmf_mapping from https://github.com/diffpy/diffpy.nmf_mapping/blob/main/diffpy/nmf_mapping/tests/data and see whether the code works.

[bobleesj]

Noticed that data are provided under examples/mix___ZnSe-w_0.4___BaTiO3_c-w_0.6 Have you tried running the package with these data? @Fil158

[sbillinge]

if the data are small, we can add it to the repo to make it easy for users.