Fixes for iOS8

Added `requestWhenInUseAuthorization` call for `CLLocationManager` to prompt for user location and updated readme.
You can see [Apple doc](https://developer.apple.com/library/ios/documentation/corelocation/reference/CLLocationManager_Class/index.html#//apple_ref/occ/instm/CLLocationManager/requestWhenInUseAuthorization) for more info.