Update Readme With New Start/End Object Syntax
Update Readme With New Start/End Object Syntax

#129 changed the syntax for start/end but neglected to update the example in the readme.
react-native-community/react-native-linear-gradient,react-native-community/react-native-linear-gradient,react-native-community/react-native-linear-gradient,react-native-community/react-native-linear-gradient