Adjust dataset card

Add description for isnnn_400.seed01 dataset.

Organize files according to https://huggingface.co/docs/datasets/main/en/repository_structure

Change 'samples' column type from fixed_len_binary_array to binary_array because the former is not supported by HF.

IsNNN400 dataset

Add XXZ300 seed=5 d_test and d_train

Put yaml metadata at the top of README.md

Add basic info and TODOs to README

initial commit