Updates steps explaining header_search_paths
Updates steps explaining header_search_paths

The React Native module is actually 1 more level up in the folder structure now since the `RCTMapboxGL.xcodeproj` is in the nested `ios` folder.
bsudekum/react-native-mapbox-gl,bsudekum/react-native-mapbox-gl,bsudekum/react-native-mapbox-gl,bsudekum/react-native-mapbox-gl