QQuickTreeViewDelegate: add some docs about pointer handlers

Change-Id: I7590d07359a09408274bc7e355aad3f754c80b34
Reviewed-by: Shawn Rutledge <shawn.rutledge@qt.io>

src/quicktemplates2/qquicktreeviewdelegate.cpp

@@ -99,6 +99,39 @@ QT_BEGIN_NAMESPACE
     is controlled with \l [QML]{Control::}{spacing}. And the space to the right of the
     contentItem is controlled with \l rightMargin.
 
+    \section2 Interacting with pointers
+    TreeViewDelegate inherits \l AbstractButton. This means that it will emit signals
+    such as \l {AbstractButton::clicked()}{clicked} when the user clicks on the delegate.
+    If needed, you could connect to that signal to implement application specific
+    functionality, in addition to the default expand/collapse behavior (and even set \l
+    {QQuickTableView::pointerNavigationEnabled}{pointerNavigationEnabled} to \c false, to
+    disable the default behavior as well).
+
+    But the AbstractButton API does not give you information about the position of the
+    click, or which modifiers are being held. If this is needed, a better approach would
+    be to use pointer handlers. To ensure that they don't interfere with the
+    existing logic in TreeViewDelegate, install them on a child item, e.g:
+
+    \code
+    TreeView {
+        id: treeView
+        delegate: TreeViewDelegate {
+            Item {
+                anchors.fill: parent
+                TapHandler {
+                    acceptedModifiers: Qt.ControlModifier
+                    onTapped: {
+                        if (treeView.isExpanded(row))
+                            treeView.collapseRecursively(row)
+                        else
+                            treeView.expandRecursively(row)
+                    }
+                }
+            }
+        }
+    }
+    \endcode
+
     \sa TreeView
 */