title: How to add a title to the color key on a contourplot?
body: <p>How does one add a title to the color key in a lattice contourplot?</p>
  
  <pre><code>library(lattice)
  contourplot(volcano, region=T, main='title')
  </code></pre>
  
  <p><a href="https://i.stack.imgur.com/0pKzl.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/0pKzl.jpg" alt="enter image description here"></a></p>
  
  <p>I've searched the documentation and don't see anything about text or titles for the <code>colorkey</code> argument or in any of the other contourplot/levelplot options.</p>