title: R ggplot add text above plot
body: <p>My data consists of the variables <code>log R ratio</code>, <code>sample_id</code> and <code>replicate</code>.
  I have made a boxplot with ggplot.</p>
  
  <pre><code>replicate_to_R$replicate &lt;-factor(replicate_to_R$replicate, levels=c( "3", "4", "8","12" ), labels=c("3", "4", "8","12"))
  
  replicate_to_R$sample_id &lt;-factor(replicate_to_R$sample_id, levels=c(74,76,78,79,80), labels=c(18,20,22,23,24))
  # boxplot
  ggplot(aes(y=logRratio, x=sample_id, fill=replicate), data=replicate_to_R) + 
  geom_boxplot(outlier.shape=NA) + scale_y_continuous(limits=c(-1,1)) + 
  scale_fill_manual(values=c("steelblue4","steelblue3","steelblue2","steelblue1")) + theme(panel.grid.major.x =element_blank()) + 
  theme(panel.background = element_blank()) + 
  theme(axis.text = element_text(size=14, color="black")) 
  </code></pre>
  
  <p>I want to add information on call rate for each sample in the top of the plot. Is there a way to add this additional information to the plot?</p>