title: Adding points on a geom_line plot
body: <p>Using an idea from a <a href="https://stackoverflow.com/questions/3550341/gantt-charts-with-r/3556020#3556020">previous question</a> I have created a gantt-like chart using ggplot2. Here is the example code:</p>
  
  <pre><code>tasks &lt;- c("Review literature", "Mung data", "Stats analysis", "Write Report")
  
  dfr &lt;- data.frame(
    name        = tasks[c(1,2,3,4,2,3)],
    start.date  = c("24/08/2010", "01/10/2010", "01/11/2010", "14/02/2011","15/12/2010","1/9/2010"),
    end.date    = c("31/10/2010", "14/12/2010", "28/02/2011", "30/04/2011","05/02/2011","1/11/2010"),
    type = c(TRUE, FALSE, TRUE, TRUE,TRUE,FALSE)
  )
  
  mdfr &lt;- melt(dfr, measure.vars = c("start.date", "end.date"))
  
  ggplot(mdfr, aes(as.Date(value, "%d/%m/%Y"), name, colour = type)) + 
    geom_line(size = 6) +
    xlab("") + ylab("") +
    theme_bw()
  </code></pre>
  
  <p>Now, I need to indicate one (or maybe more, some other day) specific critical date for each task, using a bullet or a star or anything, which maybe inside or outside the bar and also a textual annotation of that date. Can it be achieved using the above procedure. If not, is there another (not ggplot) way of doing this?  </p>
  
  <p>Thank you!</p>