title: Adding legend to barplot
body: <p>I have a simple barplot:</p>
  
  <pre><code>xtabs(~ df$Variable + df$Country)
  tab &lt;- xtabs(~ df$Variable + df$Country)
  barplot(tab, las=1, yaxp=c(0, 100, 5), ylim=c(0, 100), ylab='Variable', col=c("red","darkblue"))
  </code></pre>
  
  <p>How can I add a legend to the barplot?</p>