Add a warning to the g_dbus_connection_set_exit_on_close docs

Tell people to not leak their apps out of the session.

gio/gdbusconnection.c

@@ -2718,6 +2718,13 @@ g_dbus_connection_new_for_address_sync (const gchar           *address,
  * closed by the remote peer. See #GDBusConnection:exit-on-close for
  * more details.
  *
+ * Note that this function should be used with care. Most modern UNIX
+ * desktops tie the notion of a user session the session bus, and expect
+ * all of a users applications to quit when their bus connection goes away.
+ * If you are setting @exit_on_close to %FALSE for the shared session
+ * bus connection, you should make sure that your application exits
+ * when the user session ends.
+ *
  * Since: 2.26
  */
 void