Update README.md

GMSServices won't work if we don't import GoogleMaps.h

Author: stealkiller06

README.md

@@ -109,6 +109,8 @@ ENV['RCT_NEW_ARCH_ENABLED'] = '0'
 To set up, specify your API key in the application delegate `ios/Runner/AppDelegate.m`:
 
 ```objective-c
+#import <GoogleMaps/GoogleMaps.h>
+
 @implementation AppDelegate
 
 - (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
@@ -119,6 +121,8 @@ To set up, specify your API key in the application delegate `ios/Runner/AppDeleg
 
 ```
 
+
+
 ## Usage
 
 ### Initializing Navigation