title: Adding simple legend to plot in R
body: <p>I would like to create a very simple plot.
  I am using <a href="https://dl.dropbox.com/u/22681355/a.csv" rel="noreferrer">this data</a>: </p>
  
  <pre><code>a &lt;- read.table("https://dl.dropbox.com/u/22681355/a.csv", sep=',', header=TRUE)
  
  plot(a$X25, type="l",col="red", ylim=c(0,100))
  lines(a$X25.1, type="l", col="blue")
  lines(a$X25.2, type="l", col="green")
  lines(a$X25.3, type="l", col="brown")
  </code></pre>
  
  <p>Now I would like to add a simple legend that indicates which color is which variable.</p>
  
  <p>I understand that I can use the <code>legend()</code> command, but my problem is that I don't know how to put colors next to the text in the legend.</p>
  
  <p>What's the simplest command that would do this?</p>