refactor(site, templates): use non-single tag

site/src/pages/index.html

@@ -33,7 +33,8 @@
         </p>
         <code-block>npm create <strong style="color: var(--color-blue)">mcfly</strong>@latest</code-block>
         <p>
-          Here's a sample interactive custom element: <vanilla-hello-world />
+          Here's a sample interactive custom element:
+          <vanilla-hello-world></vanilla-hello-world>
         </p>
         <p>
           Start at the very basic of writing HTML files and enhance with

templates/basic/src/pages/index.html

@@ -25,7 +25,8 @@
     <main>
       <h2>Welcome to {{ project.name }}</h2>
       <p>
-        Here's a vanilla custom element: <vanilla-hello-world />
+        Here's a vanilla custom element:
+        <vanilla-hello-world></vanilla-hello-world>
       </p>
       <code-block language="js">
 class HelloWorld extends HTMLElement {