fix: Add a note about Grid's refresh behavior (vaadin#3735)

Add note about Grid refresh behavior when using async updates.

Co-authored-by: edler-san <19165931+edler-san@users.noreply.github.com>

Author: TatuLund

articles/flow/binding-data/data-provider.adoc

@@ -432,6 +432,9 @@ Button modify = new Button("Modify data", e -> {
 
 Alternatively, if you've bound a mutable [classname]`List` to your component, you can use helper methods in the list data view to add or remove items. You can also get an item count by hooking to the item count change event or request the item count, directly.
 
+[NOTE]
+`Grid` is a component with complex server and client interactions. For example, when you update a `Grid` by using [methodname]`Grid.getDataProvider().refreshAll()`, the `Grid` reports this to the server. Hence, there's a request to the server. For example, if you periodically update a `Grid` from a background thread, the application won't be idling, and the session won't time out.
+
 For example, it's possible to use a mutation method and listen for an item count change through the list data view, as follows:
 
 [source,java]