title: How to rotate only text in annotation in ggplot?
body: <p>I have a plot like this:</p>
  
  <pre><code>fake = data.frame(x=rnorm(100), y=rnorm(100))
  
  ggplot(data=fake, aes(x=x, y=y)) + geom_point() + theme_bw() +
    geom_vline(xintercept=-1, linetype=2, color="red") +
    annotate("text", x=-1, y=-1, label="Helpful annotation", color="red")
  </code></pre>
  
  <p><img src="https://i.stack.imgur.com/vT1Z5.jpg" alt="enter image description here"></p>
  
  <p>How would I rotate just the annotated text 90 degrees so that it is parallel to the reference line?</p>