discuss `pannable` action

`export function pannable(node: HTMLElement): ReturnType<Action>`

Creates `panstart`, `panmove`, `panend` events so you can drag elements. 

```svelte
<div class="box"
	use:pannable
	on:panstart={handlePanStart}
	on:panmove={handlePanMove}
	on:panend={handlePanEnd}
></div>
```

Demo: https://svelte.dev/tutorial/actions