Update README.md

Deleted data/processed/weighted_average_calculated_raw/FA_tracts_220.csv, data/processed/weighted_average_calculated_raw/L1_tracts_220.csv, data/processed/weighted_average_calculated_raw/MD_tracts_220.csv, data/processed/weighted_average_calculated_raw/RD_tracts_220.csv, data/processed/weighted_average_calculated_raw/ficvfWatWM_tracts_220.csv, data/processed/weighted_average_calculated_raw/fisoWatWM_tracts_220.csv, data/processed/weighted_average_calculated_raw/odiWatWM_tracts_220.csv, data/raw/weighted_averages/subjects.txt, data/raw/weighted_averages/tracts_FA.csv, data/raw/weighted_averages/tracts_L1.csv, data/raw/weighted_averages/tracts_MD.csv, data/raw/weighted_averages/tracts_RD.csv, data/raw/weighted_averages/tracts_ficvfWatWM.csv, data/raw/weighted_averages/tracts_fisoWatWM.csv, data/raw/weighted_averages/tracts_odiWatWM.csv files