app/views/layouts/application.html.erb
<!DOCTYPE html>
<html>
<head>
<title>DeviseBootstrapViews</title>
<%= stylesheet_link_tag 'application', media: 'all', 'data-turbolinks-track' => true %>
<%= javascript_include_tag 'application', 'data-turbolinks-track' => true %>
<%= csrf_meta_tags %>
</head>
<body>
<nav class="navbar navbar-default">
<div class="container-fluid">
<div class="navbar-header">
<a class="navbar-brand" href="#">
<%= image_tag('bootstrap.png',size: "25") %>
</a>
</div>
<div class="collapse navbar-collapse" id="bs-example-navbar-collapse-1">
<ul class="nav navbar-nav navbar-right">
<% if user_signed_in? %>
<li>
<%= link_to('Logout', destroy_user_session_path, :method => :delete) %>
</li>
<% else %>
<li>
<%= link_to('Login', new_user_session_path) %>
</li>
<% end %>
</ul>
</div>
</div>
</nav>
<%= flash_messages %>
<div class="col-md-offset-2 col-md-8">
<%= yield %>
</div>
</body>
</html>