<div class="jumbotron">
  <h1>Books App</h1>
  <p class="lead">"Busquem conhecimento", Bilu, Et.</p>
</div>

<div class="row marketing">
  <% @books.in_groups_of(3).each do |books| %>
    <% books.reject(&:nil?).each do |book| %>
      <div class="col-lg-6">
        <h4><%= book %></h4>
        <p><%= book.authors %>.</p>
      </div>
    <% end %>
  <% end %>
</div>

<div class="jumbotron">
  <h1>Books App</h1>
  <p class="lead">"Busquem conhecimento", Bilu, Et.</p>
</div>

<div class="row marketing">
  <% @books.in_groups_of(2).each do |books| %>
    <% books.reject(&:nil?).each do |book| %>
      <div class="col-lg-6">
        <%= image_tag 'http://placehold.it/115x180.png', alt: book %>
        <h4><%= book %></h4>
        <p><%= book.authors %>.</p>
      </div>
    <% end %>
  <% end %>
</div>

Add cover to books and a tiny fix to index view:
Add cover to books and a tiny fix to index view:

Lines should be in group of 2.
