[MergeSemantics] added code snippet (#68123)

packages/flutter/lib/src/widgets/basic.dart

@@ -6960,6 +6960,25 @@ class Semantics extends SingleChildRenderObjectWidget {
 /// would be presented as a separate feature than the checkbox, and
 /// the user would not be able to be sure that they were related.
 ///
+/// {@tool snippet}
+/// This snippet shows how to use [MergeSemantics] to merge the semantics of
+/// a [Checkbox] and [Text] widget.
+///
+/// ```dart
+/// MergeSemantics(
+///   child: Row(
+///     children: <Widget>[
+///       Checkbox(
+///         value: true,
+///         onChanged: (bool value) => null,
+///       ),
+///       const Text("Settings"),
+///     ],
+///   ),
+/// )
+/// ```
+/// {@end-tool}
+///
 /// Be aware that if two nodes in the subtree have conflicting
 /// semantics, the result may be nonsensical. For example, a subtree
 /// with a checked checkbox and an unchecked checkbox will be