title: Create Dataframe with rows made for each string appearing in a column of another Dataframe
body: <p>If you have a dataframe as follows:</p>
  
  <pre><code>genre                 mean_average_budget
  horror thriller       x
  romance comedy        y 
  action thriller       z
  documentary           a
  comedy documentary    b
  </code></pre>
  
  <p>How could one be made in which the rows are the individual appearances of each string in the genre column?
  Eg: </p>
  
  <pre><code>genre                 mean_average_budget
  horror                h
  thriller              i 
  action                k
  documentary           l
  comedy                m
  </code></pre>