SDL: Add info on how to avoid the "Prevented in-tree build" message with CMake

SDL Commits
1 
From eec41d25de00fd9cbc7d61a48db8027a439f7e02 Mon Sep 17 00:00:00 2001
From: Sam Lantinga <[EMAIL REDACTED]>
Date: Fri, 6 Aug 2021 11:30:22 -0700
Subject: [PATCH] Add info on how to avoid the "Prevented in-tree build"
 message with CMake

---
 CMakeLists.txt | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 94a6ad10f..acaa3a26e 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -1,5 +1,5 @@
 if(${CMAKE_CURRENT_SOURCE_DIR} STREQUAL ${CMAKE_CURRENT_BINARY_DIR})
-  message(FATAL_ERROR "Prevented in-tree built. Please create a build directory outside of the SDL source code and call cmake from there")
+  message(FATAL_ERROR "Prevented in-tree built. Please create a build directory outside of the SDL source code and run \"cmake -S ${CMAKE_SOURCE_DIR} -B .\" from there")
 endif()
 
 cmake_minimum_required(VERSION 3.0.0)