title: extract duplicate values with 3 or more duplicates in a column pandas dataframe
body: <p>I'm trying to extract a dataframe which only shows duplicates with e.g 3 or more duplicates in a column. For example:</p>
  <pre><code>df = pd.DataFrame({
      'one': pd.Series(['Berlin', 'Berlin', 'Tokyo', 'Stockholm','Berlin','Stockholm','Amsterdam']),
      'two': pd.Series([1, 2, 3, 4, 5, 6, 7]),
      'three': pd.Series([8, 9, 10, 11, 12])
  })
  </code></pre>
  <p>Expected output:</p>
  <pre><code>    one     two   three
  0  Berlin    1      8
  </code></pre>
  <p>The extraction should only show the row of the first duplicate.</p>