[at-spi2-core] Fix documentation for the new mode_changed signal

[Mike Gorse <mgorse src gnome org>]

commit b0bf47c85ca221471eb366729cab37e38b60f722
Author: Mike Gorse <mgorse suse com>
Date:   Thu Jun 11 14:27:28 2020 -0500

    Fix documentation for the new mode_changed signal

 atspi/atspi-accessible.c | 1 +
 1 file changed, 1 insertion(+)
---
diff --git a/atspi/atspi-accessible.c b/atspi/atspi-accessible.c
index f54aa95..4be624c 100644
--- a/atspi/atspi-accessible.c
+++ b/atspi/atspi-accessible.c
@@ -299,6 +299,7 @@ atspi_accessible_class_init (AtspiAccessibleClass *klass)
    * AtspiAccessible::mode-changed:
    * @atspiaccessible: the object which received the signal
    * @arg1: a boolean specifying whether the mode is being toggled on or off.
+   * @why: an optional string explaining why the mode changed.
    *
    * The signal "mode-changed" is emitted by a screen reader to indicate
    * that its mode has changed. This signal supports the following details: