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

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)