title: seaborn: How to add a second level of labels on the X axis
body: <p>I need to plot a time series. Dates on the X axis and values on the Y axsis, but I also need to specify the day of week on the X axsis.</p>
  
  <pre><code>ax = sns.lineplot(x='date', y='value', data=df)
  </code></pre>
  
  <p>I expect to be able to add day of week (another column from df) on the X axis.
  <a href="https://i.stack.imgur.com/sx3ii.png" rel="nofollow noreferrer">example with Excel</a></p>