title: drop down list for Cocoa textfield
body: <p>ok, I'm pretty new to objective-c. I want to create a textfield that a user is able to write the name of a country. But as the user writes in the text field I want to show a drop down list of all the countries.
  For example if the user writes on the textfield the letter "U" then the list will show all the countries that start with the letter "u".</p>
  
  <p>Does anyone knows how to implement this code?</p>