Progress bar in "preprocessing/create_sinograms.py"

[hojunieee]

1. Add following line to import tqdm

• "from tqdm import tqdm"

2. Change the for loop line

• Before: for example_index in range(len(file_list)):
• After: for example_index in tqdm(range(len(file_list)), desc="Processing files", unit="file"):

-> For short folder, this is useless, bc MPI part takes longer than the actual main function. However when processing entire brain dataset, I think this might be useful..?