Update appsettings.adoc

Added note regarding incompatibility between Java AWT and LWJGL3.

docs/modules/core/pages/system/appsettings.adoc

@@ -36,6 +36,8 @@ WARNING: The settings are saved based on the title of your game (default = "`jMo
 
 This example toggles the settings to fullscreen while the game is already running. Then it restarts the game context (not the whole game) which applies the changed settings.
 
+WARNING: The code below uses the Java AWT, which in incompatible with LWJGL3 on the Mac. Attempting to use both may cause an application UI to become unresponsive. Exact results may vary depending on what AWT features are used, when they are used, and/or which version of the MacOS, Java, and jME is used.
+
 [source,java]
 ----
 public void toggleToFullscreen() {