site: actions tutorial: destroy is not required (#2776)

Author: Conduitry

site/content/tutorial/12-actions/01-actions/text.md

@@ -27,7 +27,7 @@ import { pannable } from './pannable.js';
 ></div>
 ```
 
-Open the `pannable.js` file. Like transition functions, an action function receives a `node` and some optional parameters, and returns an action object. That object must have a `destroy` function, which is called when the element is unmounted.
+Open the `pannable.js` file. Like transition functions, an action function receives a `node` and some optional parameters, and returns an action object. That object can have a `destroy` function, which is called when the element is unmounted.
 
 We want to fire `panstart` event when the user mouses down on the element, `panmove` events (with `dx` and `dy` properties showing how far the mouse moved) when they drag it, and `panend` events when they mouse up. One possible implementation looks like this:
 
@@ -84,4 +84,3 @@ export function pannable(node) {
 Update the `pannable` function and try moving the box around.
 
 > This implementation is for demonstration purposes — a more complete one would also consider touch events.
-