Doc: Update HorizontalHeaderView Documentation of the property textRole

The textRole property in HorizontalHeaderView doc is not applicable when the custom delegate is defined.

Update documentation HorizontalHeaderView::textRole. textRole is not applicable when the custom delegate is defined by the developer.

Fixes: QTBUG-131322
Change-Id: Iafda84d97d5cae3fd769561c3a048029e5a0d50e
Reviewed-by: Paul Wicking <paul.wicking@qt.io>

src/quickcontrols/doc/src/includes/qquickheaderview.qdocinc

@@ -72,6 +72,10 @@ This property holds the model role used to display text in each header cell.
 When the model has multiple roles, textRole can be set to determine which
 role should be displayed.
 
+It is the delegate's responsibility to respect the assigned \a textRole
+when presenting data from the model.While \l HeaderViewDelegate handles this automatically,
+custom delegates must implement this behavior explicitly.
+
 If model is a QAbstractItemModel then it will default to "display"; otherwise
 it is empty.