atspicontext: Log more helpful warnings when the a11y bus doesn't exist

gtk/a11y/gtkatspicontext.c

@@ -1648,7 +1648,9 @@ get_bus_address_dbus (GdkDisplay *display)
                                   &error);
   if (error != NULL)
     {
-      g_warning ("Unable to acquire the address of the accessibility bus: %s",
+      g_warning ("Unable to acquire the address of the accessibility bus: %s. "
+                 "If you are attempting to run GTK without a11y support, "
+                 "GTK_A11Y should be set to 'none'.",
                  error->message);
       g_error_free (error);
     }