title: zipWithIndex rdd with initial value
body: <p>I have a RDD like this:</p>
  
  <pre><code>+----------+--------+
  |firstName |lastName|
  +----------+--------+
  |      john|   smith|
  |      anna|  tourde|
  +----------+--------+
  </code></pre>
  
  <p>I wouldLike to create a new column as we can do with zipWithIndex but giving and initial value of 8.</p>
  
  <pre><code>+----------+--------+-----+
  |firstName |lastName|index|
  +----------+--------+-----+
  |      john|   smith|    8|
  |      anna|  tourde|    9|
  +----------+--------+-----+
  </code></pre>
  
  <p>Do you have any idea? Thanks</p>