Training Data for Decision Tree Practical in reading-ml-chemistry repo

This is a dataset that can be used to train a decision tree to predict the band gap of a material. The data is associated with a notebook for running the practical and it can be found at https://github.com/keeeto/reading-ml-chemistry.

The data originally comes from the Materials Project.

A new muon spectroscopy dataset is added. It is from - Machine learning approach to muon spectroscopy analysis - https://iopscience.iop.org/article/10.1088/1361-648X/abe39e/meta