Update README with bitcode and Xcode requirements
Update README with bitcode and Xcode requirements

apascual/braintree_ios,braintree/braintree_ios,apascual/braintree_ios,billCTG/braintree_ios,braintree/braintree_ios,braintree/braintree_ios,apascual/braintree_ios,billCTG/braintree_ios,apascual/braintree_ios,billCTG/braintree_ios,billCTG/braintree_ios,Feverup/braintree_ios,Feverup/braintree_ios,billCTG/braintree_ios,braintree/braintree_ios,Feverup/braintree_ios,Feverup/braintree_ios