title: Callout text in R
body: <p>I want add callout text to my R-plot. For example, I have some plot:</p>
  
  <pre><code>x &lt;- seq(0, 2, by=0.1)
  y &lt;- x*x
  plot(x, y, type="l")
  </code></pre>
  
  <p><img src="https://i.stack.imgur.com/mdL6K.png" alt="enter image description here"></p>
  
  <p>I want to add some callout text like this:</p>
  
  <p><img src="https://i.stack.imgur.com/NErDr.png" alt="enter image description here"></p>
  
  <p>There are some standard methods for it?</p>