title: Split Column containing lists into different rows in pandas
body: <p>I have a dataframe in pandas like this:</p>
  
  <pre><code>id     info
  1      [1,2]
  2      [3]
  3      []
  </code></pre>
  
  <p>And I want to split it into different rows like this:</p>
  
  <pre><code>id     info
  1      1 
  1      2 
  2      3 
  3      NaN
  </code></pre>
  
  <p>How can I do this?</p>