start adding else-if chapter

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

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+<script>
+	let x = 7;
+</script>
+
+{#if x > 10}
+	<p>{x} is greater than 10</p>
+{:else}
+	{#if 5 > x}
+		<p>{x} is less than 5</p>
+	{:else}
+		<p>{x} is between 5 and 10</p>
+	{/if}
+{/if}

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

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+<script>
+	let x = 7;
+</script>
+
+{#if x > 10}
+	<p>{x} is greater than 10</p>
+{:else if 5 > x}
+	<p>{x} is less than 5</p>
+{:else}
+	<p>{x} is between 5 and 10</p>
+{/if}

site/content/tutorial/03-logic/03-else-if-blocks/text.md

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+---
+title: Else-if blocks
+---
+
+Just like in JavaScript, we can 'chain' related conditional blocks together:
+