title: ggplot2: Annotate stacked bars with totals for each bar
body: <p>I would like to annotate a plot so as to show the totals for each column. For example</p>
  
  <pre><code> ggplot(diamonds, aes(clarity, fill=cut)) + 
          geom_bar(position="fill") +
          scale_y_continuous(name="proportion")
  </code></pre>
  
  <p>This will produce a stacked barplot. However it is difficult to know what is n for each of the bars. I1,SI2 and so on. How can I annotate it so that, for each bar, n is displayed at the top? </p>