Update text.md

Added a suggestion for a user to add the preventDefault modifier so they could press any key uninterrupted by the default behavior of a key or key combination.

site/content/tutorial/16-special-elements/03-svelte-window/text.md

@@ -8,4 +8,9 @@ On line 33, add the `keydown` listener:
 
 ```html
 <svelte:window on:keydown={handleKeydown}/>
-```
+```
+Don't forget to add `preventDefault` modifier if you want to press any other key, e.g. after you have pressed `Tab` or `Ctrl + D`:
+
+```html
+<svelte:window on:keydown|preventDefault={handleKeydown}/>
+```