title: How to add number of observation in bar plot? (need to display error bar and significance together)
body: <p>I'm constructing my own graph by following the codes in a tutorial: </p>
  
  <pre><code>library(ggpubr)
  data("ToothGrowth")
  ggbarplot(ToothGrowth, x = "dose", y = "len", 
            add = c("mean_se", "jitter"),
            color = "supp", palette = "jco",
            position = position_dodge(0.8))
  </code></pre>
  
  <p>I want to show the number of observation on each column (on the bottom or on the top), together with the error bar and significance. Could anyone use ToothGrowth as an example to plot like this?</p>
  
  <p><a href="https://i.stack.imgur.com/cITjB.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/cITjB.jpg" alt="displaying n number at the bottom"></a></p>