update README
update README

Guokr1991/QIBA-DigitalPhantoms,Guokr1991/QIBA-DigitalPhantoms,RSNA-QIBA-US-SWS/QIBA-DigitalPhantoms,Guokr1991/QIBA-DigitalPhantoms,RSNA-QIBA-US-SWS/QIBA-DigitalPhantoms,RSNA-QIBA-US-SWS/QIBA-DigitalPhantoms