QMP: Improve RTC_CHANGE event description

Some people might think that this event is emitted whenever the
time changes, be more specific.

Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>
diff --git a/QMP/qmp-events.txt b/QMP/qmp-events.txt
index a94e9b4..c084a47 100644
--- a/QMP/qmp-events.txt
+++ b/QMP/qmp-events.txt
@@ -41,7 +41,7 @@
 RTC_CHANGE
 ----------
 
-Emitted when the RTC time changes.
+Emitted when the guest changes the RTC time.
 
 Data: