title: append specific amount of empty rows to pandas dataframe
body: <p>I want to append a specific amount of empty rows to that  df</p>
  <pre><code>df = pd.DataFrame({'cow': [2, 4, 8],
                    'shark': [2, 0, 0],
                    'pudle': [10, 2, 1]})
  
  </code></pre>
  <p>with <code>df = df.append(pd.Series(), ignore_index = True)</code> I append one empty row, how can I append x amount of rows ?</p>