Add dynamic condition result on App.svelte

I added the dynamic condition result example. It would be nice to showing this basic example on the tutorial, Svelte can do many things that is easy to understand even with the beginner.

site/content/tutorial/04-logic/03-else-if-blocks/app-b/App.svelte

@@ -1,5 +1,8 @@
 <script>
 	let x = 7;
+	function incrementNumber() {
+		x += 1;
+	};
 </script>
 
 {#if x > 10}
@@ -9,3 +12,7 @@
 {:else}
 	<p>{x} is between 5 and 10</p>
 {/if}
+
+<button on:click={incrementNumber}>
+	Add number
+</button>