Add reference to UnserializableComponentWrapper

See also: https://github.com/vaadin/docs/pull/4118/files

articles/components/spreadsheet/index.adoc

@@ -338,7 +338,7 @@ The Vaadin Spreadsheet has a few inherent limitations. Below is a list of them:
 * No provided toolbars, menus, or other controls for formatting cells.
 * Limited support for the older XSL formats.
 * Constraints related to Apache POI, such as importing and exporting Excel files.
-* The component is not serializable due to the internal usage of Apache POI. The `@PreserveOnRefresh` annotation and session replication with Kubernetes Kit are not supported when using Spreadsheet.
+* The component is not serializable due to the internal usage of Apache POI. The `@PreserveOnRefresh` annotation. Replication with Kubernetes Kit requires to use UnserializableComponentWrapper when using Spreadsheet.
 * The SUBTOTAL formula is limited to aggregate functions that do not ignore hidden values (i.e., function codes from 1 to 7, as well as 9) because they are not implemented in Apache POI.
 * Strict OOXML format is not supported by Apache POI.
 * No support for theming the component the same way as other Vaadin components.