title: How to add subtext to axes in ggplot2 R
body: <p>For the main y-axis and x-axis, I have generic titles like "Tank's Ratio" and "Counts". I want a second line of label where I specify the ratio and counts. eg. Just below "Tank's Ratio" I want "# in water/# in sand" in a smaller font but along the y-axis. Similarly for the x-axis.
  Here is the basic code</p>
  
  <pre><code>data &lt;- data.frame(set = c(1, 1, 1, 2, 2, 3, 3, 3, 3, 3, 4, 4), density = c(1, 3, 3, 1, 3, 1, 1, 1, 3, 3, 1, 3), counts = c(100, 2, 3, 76, 33, 12, 44, 13, 54, 36, 65, 1), ratio = c(1, 2, 3, 4, 1, 2, 3, 4, 5, 6, 90, 1))
  
  library(ggplot2)
  
  ggplot(data, aes(x = counts, y = ratio)) + 
    geom_point() + 
    ylab("Tank's Ratio") + 
    xlab("Counts") 
  </code></pre>