title: how to annotate subplot python
body: <p>I am trying to annotate a subplot.
  I would like to put a letter inside the plot so to help when I will write the caption..</p>
  
  <p>so far I am trying in this way.
  no results.
  any help?</p>
  
  <pre><code>fname='SHOT_'+str(shot)
  plt.figure(fname)
  ftitle='Time Traces - '+str(nshot[i])
  plt.suptitle(ftitle, fontsize=11)
  
  #PLOT 1
  ax1 = plt.subplot(711)
  # xy = get_axis_limits(ax1)
  # print(xy)
  
  
  plt.scatter(timetraces['Time_LID3'], savitzky_golay(np.array(timetraces['KG1V/LID3']), 17, 1),color='red', label="KG1V",s=10)
  fxlabel='Time [s]'
  fylabel='$part/m^{-2}$'
  plt.locator_params(axis='y',nbins=4)
  # plt.xlabel(fxlabel,{'color': 'k','size': 11})
  plt.ylabel(fylabel,{'color': 'k','size': 8})
  plt.setp(ax1.get_xticklabels(), visible=False)
  plt.legend(prop={'size':8})
  ax1.yaxis.set_minor_locator(AutoMinorLocator())
  ax1.xaxis.set_minor_locator(AutoMinorLocator())
  ax1.annotate('G', xy=get_axis_limits(ax1))
  plt.subplots_adjust(wspace=0, hspace=0)
  plt.show()
  </code></pre>