Document QCalendarBackend::name()

Neglected previously.

Pick-to: 5.15
Change-Id: I0acd9f77d1623a1fcd8766f734c350316401b3a9
Reviewed-by: Paul Wicking <paul.wicking@qt.io>

src/corelib/time/qcalendar.cpp

@@ -202,9 +202,16 @@ QCalendar::System QCalendarBackend::calendarSystem() const
     return QCalendar::System::User;
 }
 
+/*!
+    \fn QString QCalendarBackend::name() const;
+
+    This pure virtual method should be overloaded by each backend implementation
+    to return the name that the backend passes to the base-class as its name.
+*/
+
 /*!
     The primary name of this calendar.
- */
+*/
 QString QCalendar::name() const
 {
     return d ? d->name() : QString();