SDL: Updated the migration guide to note that you can check the return value of SDL_AddEventWatch()

SDL Commits
1 
From 274da8561c1578f05852f29b4d0d31201cc3820d Mon Sep 17 00:00:00 2001
From: Sam Lantinga <[EMAIL REDACTED]>
Date: Sat, 4 Nov 2023 10:42:28 -0700
Subject: [PATCH] Updated the migration guide to note that you can check the
 return value of SDL_AddEventWatch()

---
 docs/README-migration.md | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/docs/README-migration.md b/docs/README-migration.md
index e9ea32828238..bbe1fe56d83f 100644
--- a/docs/README-migration.md
+++ b/docs/README-migration.md
@@ -314,6 +314,8 @@ The gamepad event structures caxis, cbutton, cdevice, ctouchpad, and csensor hav
 
 SDL_QUERY, SDL_IGNORE, SDL_ENABLE, and SDL_DISABLE have been removed. You can use the functions SDL_SetEventEnabled() and SDL_EventEnabled() to set and query event processing state.
 
+SDL_AddEventWatch() now returns -1 if it fails because it ran out of memory and couldn't add the event watch callback.
+
 The following symbols have been renamed:
 * SDL_APP_DIDENTERBACKGROUND => SDL_EVENT_DID_ENTER_BACKGROUND
 * SDL_APP_DIDENTERFOREGROUND => SDL_EVENT_DID_ENTER_FOREGROUND