title: text caption not appearing matplotlib
body: <p>I cannot understand why my text caption does not appear on my plot.  I am finding the documentation pretty confusing about the order of placement for the legend and caption labels.. </p>
  
  <p>My code is here, I don't know what is wrong. Everything is appearing as I would expect (title, axes labels, date format, ...) except the text for the caption is not on there at all.</p>
  
  <pre><code>fig = plt.figure(figsize=(24, 12), dpi=60)
  ax = fig.add_subplot(111)
  plt.plot(datetime_series,ws_cumsum_mean1,label='1979-1994')
  plt.plot(datetime_series,ws_cumsum_mean2,label='1996-2005')
  plt.plot(datetime_series,ws_cumsum_mean3,label='2006-2014')
  txt = '''Caption text'''
  plt.legend(loc='best')
  </code></pre>
  
  <p>this is where I try to add the caption:</p>
  
  <pre><code>ax.text(0.5,-0.5,txt,transform=ax.transAxes)
  </code></pre>
  
  <p>.</p>
  
  <pre><code>plt.gca().xaxis.set_major_formatter(mdates.DateFormatter('%d-%m'))
  plt.ylabel('Y label title')
  plt.xlabel('X label title')
  plt.title('Plot title')
  </code></pre>