title: Add text to generated quadrant area by x and y plot lines , highcharts
body: <p>I have a scatter chart  to demonstrate some load from the servers with two dimensions , x and y. </p>
  
  <p>And I will define two plot lines to show if the point is overload, which is like the demo shows(just a quick demo , so I just copy the link):</p>
  
  <pre><code>"http://codepen.io/anon/pen/xZprWa"
  </code></pre>
  
  <p>while, I also need to demonstrate that what is the  generated quadrant means with some labels simply like:</p>
  
  <p><a href="https://i.stack.imgur.com/XgyMh.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/XgyMh.png" alt="enter image description here"></a></p>
  
  <p>But I can't find any methods/options from the api to achieve this, is there any simple method to do this? Like find the position and put a label to it will absolute position? </p>