title: Simple cropping with Paperclip
body: <p>I would like to crop images on upload using Paperclip to get square thumbs from the center of the original picture. I find out a method in documentation that seems to do exactly what I want:</p>
  
  <p><a href="http://dev.thoughtbot.com/paperclip/classes/Paperclip/Geometry.html" rel="noreferrer">transformation_to(dst, crop = false)</a></p>
  
  <p>The problem is that I can't figure out where to use this method. It would be great to simply pass something as a parameter here:</p>
  
  <pre>  has_attached_file :picture, 
                      :styles => { :medium => "600x600>", :thumb => "something here" }</pre>