How to add a legend to the plots? For example, if using several moving averages it will be useful to show a legend to map moving averages to line plots. Is clear how this is done using matplotlib but ...

I'd like to be able to add the QuiverKey object to the legend as a handle. So the length of the arrow in the legend is meaningful to the quivers on the plot, but so it can be displayed in a tidy way ...