title: How to add custom attribute (checkbox)?
body: <p>I can add a checkbox by editing the following file manually:</p>
  
  <pre><code>app/design/adminhtml/default/default/template/sales/order/view/info.phtml
  </code></pre>
  
  <p>but how can I add an custom attribute (checkbox) without editing this file via magento module and how to save the value to database?</p>
  
  <p>I already know how to create a module but I just dont get, how to create custom attribute with magento modules.</p>
  
  <p>I really need some advice, where to begin or how. </p>