title: Bokeh add label to second axis on the right
body: <p>I am creating a bar chart using <a href="http://bokeh.pydata.org" rel="noreferrer">Bokeh</a>, and I want to display 2 independent sets of data. I have <a href="https://stackoverflow.com/a/30914348/3585557">added another y-axis to the right side of my plot</a> using the following</p>
  
  <pre><code>bar2.extra_y_ranges = {"Mtons": Range1d(start=0, end=2000)}
  bar2.add_layout(LinearAxis(y_range_name="Mtons"), 'right')
  </code></pre>
  
  <p>How do I add a label for the second axis?</p>