title: Pandas insert empty row at 0th position
body: <p>Suppose have following data frame</p>
  
  <pre><code>        A   B   
  1   2   3   4   5
  4   5   6   7   8
  </code></pre>
  
  <p>I want to check if <code>df(0,0)</code> is <code>nan</code> then insert pd.series(np.nan) at 0th position. So in above case it will be </p>
  
  <pre><code>        A   B   
  
  1   2   3   4   5
  4   5   6   7   8
  </code></pre>
  
  <p>I am able to check <code>(0,0)</code> element but how do I insert empty row at first position?</p>