added `self` modifier explanation to the docs

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

@@ -23,5 +23,6 @@ The full list of modifiers:
 * `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 ([MDN docs](https://developer.mozilla.org/en-US/docs/Learn/JavaScript/Building_blocks/Events#Event_bubbling_and_capture))
 * `once` — remove the handler after the first time it runs
+* `self` — only trigger handler if event.target is the element itself
 
 You can chain modifiers together, e.g. `on:click|once|capture={...}`.