title: How to add custom options to Product Sort By drop down in Magento?
body: <p>I have developed my first Magento site and my client has asked me to do something I cannot
  figure out how to do.</p>
  
  <p>Currently, in any given category, the product Sort By dropdown contains the following options:</p>
  
  <pre><code>Position
  Name
  Price
  </code></pre>
  
  <p>I need to change that to:</p>
  
  <pre><code>Relevance
  Popular
  Price
  </code></pre>
  
  <p>How do I do this?</p>