📝 Add docs for hideHandlesWhenNotResizable

Author: BirjuVachhani

docs/handles.mdx

@@ -38,6 +38,22 @@ the interactive area is aligned to the center of box corner/side.
   );
 ```
 
+## Handle visibility
+
+By default, handles will be hidden when `resizable` is set to `false`. This can be changed by setting
+`hideHandlesWhenNotResizable` to `false`.
+
+```dart title="Showing handles when box is not resizable"
+  TransformableBox(
+    rect: rect,
+    flip: flip,
+    resizable: false,
+    hideHandlesWhenNotResizable: false,
+    onChanged: (event) {...},
+    contentBuilder: (context, rect, flip) {...},
+  );
+```
+
 ## Customizing the default handles
 
 By default, `TransformableBox` uses `DefaultCornerHandle` and `DefaultSideHandle` to build the handles. You can