docs: Use list for nav example

Since many people may copy the example HTML wholesale, using a list inside the nav will start them out with better practices; as per [W3C tutorial](https://www.w3.org/WAI/tutorials/menus/structure/#identify-menus).

docs/content/4.api/1.components/3.content-navigation.md

@@ -18,9 +18,11 @@ The `default`{lang=ts} slot can be used to render the content with `v-slot="{ na
 <template>
   <nav>
     <ContentNavigation v-slot="{ navigation }">
-      <div v-for="link of navigation" :key="link._path">
-        <NuxtLink :to="link._path">{{ link.title }}</NuxtLink>
-      </div>
+      <ul>
+        <li v-for="link of navigation" :key="link._path">
+          <NuxtLink :to="link._path">{{ link.title }}</NuxtLink>
+        </li>
+      </ul>
     </ContentNavigation>
   </nav>
 </template>