Added short EXTTuple summary to the README
Added short EXTTuple summary to the README

sanojnambiar/libextobjc,bboyesc/libextobjc,telly/libextobjc,sunfei/libextobjc,sandyway/libextobjc,jiakai-lian/libextobjc,kolyuchiy/libextobjc,goodheart/libextobjc,WPDreamMelody/libextobjc,liuruxian/libextobjc,KBvsMJ/libextobjc