Add documentation to each dataset on download sources, and what files specifically are compatible. #883
Description
Right now, we just assume the users know where each dataset is located, and exactly what files are required.
But, MIMIC-CXR vs. MIMIC-CXR-jpg are 2 different datasets referencing the same dataset.
MIMIC-CXR-JPG is supported, but MIMIC-CXR is not.