docs: Added some notes about iOS and the main callbacks.

docs/README-ios.md

@@ -117,6 +117,9 @@ e.g.
     }
 
 
+Note that if you are using main callbacks instead of a standard C main() function, your SDL_AppEvent() callback will run as these events arrive and you do not need to use SDL_SetEventFilter.
+
+
 Notes -- Accelerometer as Joystick
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@@ -255,6 +258,9 @@ e.g.
     }
 
 
+Note that if you are using main callbacks instead of a standard C main() function, your SDL_AppIterate() callback is already doing this and you don't need to use SDL_iOSSetAnimationCallback.
+
+
 Deploying to older versions of iOS
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