title: Draw a line at specific position/annotate a Facetgrid in seaborn
body: <p>A have produced a boxplot with Facetgrid in seaborn the following way</p>
  <pre><code># Import the dataset
  tips = sns.load_dataset(&quot;tips&quot;)
  
  # Plot using FacetGrid, separated by smoke
  plt.style.use('ggplot')
  g = sns.FacetGrid(tips, col=&quot;smoker&quot;, size=5, aspect=1.5)
  g.map(sns.boxplot, &quot;sex&quot;, &quot;total_bill&quot;, palette='viridis', order=['Male', 'Female'])
  plt.show()
  </code></pre>
  <p>I now want to draw to distinct horizontal lines in each of the plot. For instance one horizontal line (with coordinated (0,10)) <strong>only</strong> in the left-hand side plot and another horizontal line (with coordinates (0,30)) <strong>only</strong> in the right-hand side plot.</p>
  <p>How can I go about doing that?</p>