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

SDL Commits
1 
From 239b34d7601506bd7bb6ae3c663037467e9a6472 Mon Sep 17 00:00:00 2001
From: "Ryan C. Gordon" <[EMAIL REDACTED]>
Date: Sat, 13 Apr 2024 15:14:32 -0400
Subject: [PATCH] docs: Added some notes about iOS and the main callbacks.

---
 docs/README-ios.md        |  6 ++++++
 include/SDL3/SDL_system.h | 10 +++++++++-
 2 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/docs/README-ios.md b/docs/README-ios.md
index 2080f7bc680bb..33320a191c326 100644
--- a/docs/README-ios.md
+++ b/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
 ==============================================================================
 
@@ -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
 ==============================================================================
 
diff --git a/include/SDL3/SDL_system.h b/include/SDL3/SDL_system.h
index a684d07708776..0d79c7143d791 100644
--- a/include/SDL3/SDL_system.h
+++ b/include/SDL3/SDL_system.h
@@ -179,7 +179,15 @@ extern DECLSPEC int SDLCALL SDL_LinuxSetThreadPriorityAndPolicy(Sint64 threadID,
  * This function is only available on Apple iOS.
  *
  * For more information see:
- * https://github.com/libsdl-org/SDL/blob/main/docs/README-ios.md
+ *
+ * https://wiki.libsdl.org/SDL3/README/ios
+ *
+ * Note that if you use the "main callbacks" instead of a standard C `main`
+ * function, you don't have to use this API, as SDL will manage this for you.
+ *
+ * Details on main callbacks are here:
+ *
+ * https://wiki.libsdl.org/SDL3/README/main-functions
  *
  * \param window the window for which the animation callback should be set
  * \param interval the number of frames after which **callback** will be