SDL_image: Added information about how to enable the large libraries when building with CMake

From 3a23b36fb345376996003667e6dfa27d45f0c2fd Mon Sep 17 00:00:00 2001
From: Sam Lantinga <[EMAIL REDACTED]>
Date: Tue, 10 May 2022 16:46:43 -0700
Subject: [PATCH] Added information about how to enable the large libraries
 when building with CMake

---
 README.txt | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/README.txt b/README.txt
index b370502..51544cd 100644
--- a/README.txt
+++ b/README.txt
@@ -31,10 +31,12 @@ This library is under the zlib License, see the file "LICENSE.txt" for details.
 Note:
 Support for AVIF, JPEG-XL, TIFF, and WebP are not included by default because of the
 size of the decode libraries, but you can get them by running external/download.sh
-- For UNIX platforms, you can build and install them normally and the configure script
-  will pick them up and use them.
-- For Windows platforms, you will need to build them and then add the appropriate LOAD_*
-  preprocessor define to the Visual Studio project.
-- For Apple platforms, you can edit the config at the top of the project to enable them,
-  and you will need to include the appropriate framework in your application.
+- When building with CMake, you can enable the appropriate SUPPORT_* options defined
+  in CMakeLists.txt.
+- When building with configure/make, you can build and install them normally and the
+  configure script will detect and use them.
+- When building with Visual Studio, you will need to build the libraries and then add
+  the appropriate LOAD_* preprocessor define to the Visual Studio project.
+- When building with Xcode, you can edit the config at the top of the project to enable
+  them, and you will need to include the appropriate framework in your application.
 - For Android, you can edit the config at the top of Android.mk to enable them.