docs(README, v5): update ios native initialization to match new style (…

…#133)

An extra `BREAKING CHANGE` note was added to the releases entry as well

README.md

@@ -264,7 +264,7 @@ If you would like to initialize the Facebook SDK even earlier in startup for iOS
 
 - (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
 {
-  [FBSDKApplicationDelegate initializeSDK:launchOptions]; // <- add this
+  [FBSDKApplicationDelegate.sharedInstance initializeSDK]; // <- add this
 
   // your other stuff
 }