Update Layouts and Rendering in Rails [ci skip]

* The example code on this page are similar to ones generated
  by scaffold generator, but some points are different.

* Of course, it is no reason to be as same as scaffolding codes.
  But this is the guide for beginners, I thought it's better
  to be almost same as scaffolding codes.

guides/source/layouts_and_rendering.md

@@ -71,23 +71,25 @@ If we want to display the properties of all the books in our view, we can do so
 <h1>Listing Books</h1>
 
 <table>
-  <tr>
-    <th>Title</th>
-    <th>Summary</th>
-    <th></th>
-    <th></th>
-    <th></th>
-  </tr>
-
-<% @books.each do |book| %>
-  <tr>
-    <td><%= book.title %></td>
-    <td><%= book.content %></td>
-    <td><%= link_to "Show", book %></td>
-    <td><%= link_to "Edit", edit_book_path(book) %></td>
-    <td><%= link_to "Remove", book, method: :delete, data: { confirm: "Are you sure?" } %></td>
-  </tr>
-<% end %>
+  <thead>
+    <tr>
+      <th>Title</th>
+      <th>Content</th>
+      <th colspan="3"></th>
+    </tr>
+  </thead>
+
+  <tbody>
+    <% @books.each do |book| %>
+      <tr>
+        <td><%= book.title %></td>
+        <td><%= book.content %></td>
+        <td><%= link_to "Show", book %></td>
+        <td><%= link_to "Edit", edit_book_path(book) %></td>
+        <td><%= link_to "Destroy", book, method: :delete, data: { confirm: "Are you sure?" } %></td>
+      </tr>
+    <% end %>
+  </tbody>
 </table>
 
 <br>