Add link to shuffle visualization

Author: hollance

README.markdown

@@ -130,6 +130,7 @@ Often just using the built-in `Array`, `Dictionary`, and `Set` types is sufficie
 ### Lists
 
 - [Linked List](Linked List/). A sequence of data items connected through links. Covers both singly and doubly linked lists.
+- Skip List
 
 ### Trees
 

Shuffle/README.markdown

@@ -125,4 +125,6 @@ The algoritm is quite clever and I suggest you walk through an example yourself,
 
 These Swift implementations are based on pseudocode from the [Wikipedia article](https://en.wikipedia.org/wiki/Fisher–Yates_shuffle).
 
+Mike Bostock has a [great visualization](http://bost.ocks.org/mike/shuffle/) of the shuffle algorithm.
+
 *Written for Swift Algorithm Club by Matthijs Hollemans*