add README.xcode
add README.xcode

biddyweb/flexisip,gale320/flexisip,gale320/flexisip,biddyweb/flexisip,biddyweb/flexisip,BelledonneCommunications/flexisip,BelledonneCommunications/flexisip,biddyweb/flexisip,gale320/flexisip,BelledonneCommunications/flexisip,gale320/flexisip,BelledonneCommunications/flexisip