title: Is it possible to add a string as a legend item in matplotlib
body: <p>I am producing some plots in matplotlib and would like to add explanatory text for some of the data. I want to have a string inside my legend as a separate legend item above the '0-10' item. Does anyone know if there is a possible way to do this?</p>
  
  <p><img src="https://i.stack.imgur.com/TDuGh.png" alt="enter image description here"></p>
  
  <p>This is the code for my legend:<br>
  <code>ax.legend(['0-10','10-100','100-500','500+'],loc='best')</code></p>