improve readme formatting
improve readme formatting

jingruoruchu/classroom,chengjunjian/classroom,BelieveC/classroom,ConnorCartwright/classroom,guoyu07/classroom,hackerkid/classroom,mostlybadfly/classroom,BelieveC/classroom,adoosii/classroom,jingruoruchu/classroom,nfeliciano/classroom,jasnow/classroom,bhanuc/classroom,ConnorCartwright/classroom,tjhorner/classroom,jingruoruchu/classroom,chenwenbin928/classroom,bhanuc/classroom,jasnow/classroom,tjhorner/classroom,mkcode/classroom,alejandrogarciasalas/classroom,guoyu07/classroom,RyanTech/classroom,alejandrogarciasalas/classroom,adoosii/classroom,hackerkid/classroom,nfeliciano/classroom,chenwenbin928/classroom,nfeliciano/classroom,hackerkid/classroom,RyanTech/classroom,tjhorner/classroom,guoyu07/classroom,mostlybadfly/classroom,alejandrogarciasalas/classroom,BelieveC/classroom,adoosii/classroom,chenwenbin928/classroom,chengjunjian/classroom,mostlybadfly/classroom,mkcode/classroom,ConnorCartwright/classroom,RyanTech/classroom,BelieveC/classroom,mkcode/classroom,jasnow/classroom,chengjunjian/classroom,bhanuc/classroom