Add blog posts and update blog page with links

src/pages/blog.astro

@@ -16,5 +16,10 @@
     <a href='/blog/'>Blog</a>
     <h1>My Astro Learning Blog</h1>
     <p>This is where I will post about my journey learning Astro.</p>
+    <ul>
+      <li><a href='/posts/post-1/'>Post 1</a></li>
+      <li><a href='/posts/post-2/'>Post 2</a></li>
+      <li><a href='/posts/post-3/'>Post 3</a></li>
+    </ul>
   </body>
 </html>