Add implementation for the given tutorial example

site/content/tutorial/02-reactivity/04-updating-arrays-and-objects/text.md

@@ -24,3 +24,9 @@ function addNumber() {
 You can use similar patterns to replace `pop`, `shift`, `unshift` and `splice`.
 
 > Assignments to *properties* of arrays and objects — e.g. `obj.foo += 1` or `array[i] = x` — work the same way as assignments to the values themselves.
+>
+> ```js
+> function addNumber() {
+>		numbers[numbers.length] = numbers.length + 1;
+> }
+> ```