text: Title: Add description of parameter to docstring
  Body: @Haebuk had opened a PR to deal with this but closed it https://github.com/DistrictDataLabs/yellowbrick/pull/1233
  
  We just need to add this line below to the KneeLocator docstring for `y` located in yellowbrick/utils/kneed.py 
  
  "A list of k scores corresponding to each value of k. The type of k scores are determined by the metric parameter from the KElbowVisualizer class. " 
  
  https://github.com/DistrictDataLabs/yellowbrick/blob/092c0ca25187b3cde9f608a1f7bc6d8c2b998f96/yellowbrick/utils/kneed.py#L61-L62
  
  
  ```
  class KneeLocator(object):
      """
      Finds the "elbow" or "knee" which is a value corresponding to the point of maximum curvature
      in an elbow curve, using knee point detection algorithm. This point is accessible via the
      `knee` attribute.
  
      Parameters
      ----------
      x : list
         A list of k values representing the no. of clusters in KMeans Clustering algorithm.
  
      y : list
         A list of k scores corresponding to each value of k. The type of k scores are determined by the metric parameter from the KElbowVisualizer class.
  
      S : float, default: 1.0
         Sensitivity parameter that allows us to adjust how aggressive we want KneeLocator to
         be when detecting "knees" or "elbows".
  
      curve_nature : string, default: 'concave'
         A string that determines the nature of the elbow curve in which "knee" or "elbow" is
         to be found.
  
      curve_direction : string, default: 'increasing'
         A string that determines tha increasing or decreasing nature of the elbow curve in
         which "knee" or "elbow" is to be found.
  
      online : bool, default: False
          kneed will correct old knee points if True, will return first knee if False
  
      Notes
      -----
      The KneeLocator is implemented using the "knee point detection algorithm" which can be read at
      `<https://www1.icsi.berkeley.edu/~barath/papers/kneedle-simplex11.pdf>`
  ```