Use semantic HTML tags for tutorial form example (#2715)

* Indent form example

* Use semantic HTML for form example

* Add `type` attributes to inputs and button

chapters/tutorial.xml

@@ -370,9 +370,13 @@ if (str_contains($_SERVER['HTTP_USER_AGENT'], 'Firefox')) {
      <programlisting role="html">
 <![CDATA[
 <form action="action.php" method="post">
-    <p>Your name: <input type="text" name="name" /></p>
-    <p>Your age: <input type="text" name="age" /></p>
-    <p><input type="submit" /></p>
+    <label for="name">Your name:</label>
+    <input name="name" id="name" type="text">
+
+    <label for="age">Your age:</label>
+    <input name="age" id="age" type="number">
+
+    <button type="submit">Submit</button>
 </form>
 ]]>
      </programlisting>