explain once modifier

site/content/tutorial/05-events/03-event-modifiers/text.md

@@ -22,6 +22,6 @@ The full list of modifiers:
 * `stopPropagation` — calls `event.stopPropagation()`, preventing the event reaching the next element
 * `passive` — improves scrolling performance on touch/wheel events (Svelte will add it automatically where it's safe to do so)
 * `capture` — fires the handler during the *capture* phase instead of the *bubbling* phase
-* `once`
+* `once` — remove the handler after the first time it runs
 
 You can chain modifiers together, e.g. `on:click|once|capture={...}`.