title: wxpython add line to TextCtrl
body: <p>I have a multi line, read only TextCtrl in wxpython
  I know how to set values using </p>
  
  <pre><code>myTextCtrl.SetValue('hello')
  </code></pre>
  
  <p>But this will change whatever I previously had in my TextCtrl...
  How do I add a new line and keep whatever I had before?</p>