sdl2-compat: Update README.md

From ca92722063f2c0475d9aae9365b9dc75f068fa96 Mon Sep 17 00:00:00 2001
From: Curculigo <[EMAIL REDACTED]>
Date: Sun, 29 Sep 2024 12:34:01 +0700
Subject: [PATCH] Update README.md

---
 README.md | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/README.md b/README.md
index 0304b2e1..9c23bd63 100644
--- a/README.md
+++ b/README.md
@@ -76,7 +76,7 @@ If necessary, you might have to fill in the location of the SDL3 headers
 when using CMake. sdl2-compat does not need SDL3's library to _build_,
 just its headers (although it may complain about the missing library,
 you can ignore that). From the command line, add
-`-DSDL3_INCLUDE_DIR=/path/to/SDL3/include`, or find this in the CMake
+`-DSDL3_INCLUDE_DIRS=/path/to/SDL3/include`, or find this in the CMake
 GUI and set it appropriately, click "Configure" again, and then "Generate."
 
 When the build is complete, you'll have a shared library you can drop in