Minor update to warning when GLFWH is not found.

Former-commit-id: 80ff41a36cc5be9ae24dc32db7b9b43af399da82

tutorial/cmake/FindGLFWH.cmake

@@ -37,7 +37,7 @@ if(GLFW_FOUND)
   message(STATUS "Found GLFW: ${GLFW_INCLUDE_DIR} -- HEADERS ONLY")
 else(GLFW_FOUND)
   if (NOT GLFW_FIND_QUIETLY)
-    message("could NOT find GLFW")
+    message(WARNING "could NOT find GLFW")
   endif (NOT GLFW_FIND_QUIETLY)
 endif(GLFW_FOUND)