qapi: Fix up documentation for recent commit a9529100

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-Id: <20190214152251.2073-3-armbru@redhat.com>

docs/devel/qapi-code-gen.txt

@@ -1410,6 +1410,8 @@ Example:
 
     extern const QEnumLookup example_QAPIEvent_lookup;
 
+    void example_qapi_event_emit(example_QAPIEvent event, QDict *qdict);
+
     #endif /* EXAMPLE_QAPI_EVENTS_H */
     $ cat qapi-generated/example-qapi-events.c
 [Uninteresting stuff omitted...]