title: ggplot2: change font size for annotation_custom()
body: <p>I used annotation_custom() to add text below my plot. However, I cannot figure out how to decrease the font size.Desperately, I tried <code>geom_text(size= 8)</code> which did not work &amp; <code>annotation_custom(size=8)</code> does not take a 'size' argument. How do you change the font size of annotation_custom()?</p>
  
  <pre><code>df &lt;- data.frame(x=seq(1:100), y=sort(rexp(100, 2)))
  p= ggplot(df, aes(x=x, y=y)) + 
     geom_point()+
     theme(plot.margin = unit(c(1,1,3,1), "cm"))+
     ggtitle('Random Plot')
  
  Text1 = textGrob('Additional suggestions:')
  p1 = p + annotation_custom(grob = Text1,  xmin = 0.2, xmax = 0.2, ymin = -0.3, ymax = -0.3)
  
  gt &lt;- ggplotGrob(p1)
  gt$layout$clip[gt$layout$name=="panel"] &lt;- "off"
  grid.newpage()
  grid.draw(gt)
  </code></pre>
  
  <p>Any info would be super helpful, many thanks!</p>