title: nested has_one in active admin
body: <p>I'm using Rails 3.0.10 and ActiveAdmin 0.3.2. </p>
  
  <p>I have a problem with nested form and an has_one association. Using an has_many I can get nested forms but I really need to understand and use an has_one in this case.</p>
  
  <p>Model:</p>
  
  <pre><code>class Article &lt; ActiveRecord::Base
    belongs_to :section
    has_one :seo
    accepts_nested_attributes_for :seo
  end
  
  class Seo &lt; ActiveRecord::Base
    belongs_to :article
  end
  </code></pre>
  
  <p>How write app/admin/article.rb ? </p>
  
  <p>Thanks for any suggestions!</p>