app/views/admin/customers/_breadcrumb.html.erb
<ol class="breadcrumb">
<li><%= link_to "Customers", admin_customers_path %></li>
<% if current_page == "show" %>
<li class="active">Customer #<%= @customer.id.to_s %></li>
<% elsif current_page == "new" %>
<li class="active">New</li>
<% elsif current_page == "edit" %>
<li><%= link_to "Customer #"+@customer.id.to_s, admin_customer_path(@customer) %></li>
<li class="active">Edit</li>
<% end %>
</ol>