title: annotate a plot using matplotlib
body: <p>I am using this to making a plot with contains in specific moment something such as highlight</p>
  
  <pre><code>plt.axis('normal')
  plt.axvspan(76, 76, facecolor='g', alpha=1)
  plt.plot(ts.e1, 'r',linewidth=1.5)
  plt.ylabel("Anger",fontsize=14,color='blue')
  plt.ylim(ymax=0.04)
  plt.xlim(xmax=122)
  plt.grid(True)
  plt.title("Anger - Real Events", fontsize=20,color='black')
  plt.xlabel('minutes', fontsize=14, color='b')
  plt.show()
  </code></pre>
  
  <p>Is there any idea if i could add horizontal text like 'span 1' in this:</p>
  
  <pre><code>plt.axvspan(76, 76, facecolor='g', alpha=1)
  </code></pre>
  
  <p>or using the text 'line1' and have a arrow to show in this span?</p>