Add selection sort.

Author: trekhleb

src/algorithms/sorting/bubble-sort/README.md

@@ -6,3 +6,5 @@ the list to be sorted, compares each pair of adjacent
 items and swaps them if they are in the wrong order. 
 The pass through the list is repeated until no swaps 
 are needed, which indicates that the list is sorted.
+
+![Algorithm Visualization](https://upload.wikimedia.org/wikipedia/commons/c/c8/Bubble-sort-example-300px.gif)

src/algorithms/sorting/selection-sort/README.md

@@ -9,6 +9,6 @@ performance advantages over more complicated algorithms
 in certain situations, particularly where auxiliary 
 memory is limited.
 
-![Selection Sort Visualization](https://upload.wikimedia.org/wikipedia/commons/b/b0/Selection_sort_animation.gif)
+![Algorithm Visualization](https://upload.wikimedia.org/wikipedia/commons/b/b0/Selection_sort_animation.gif)
 
-![Selection Sort Visualization](https://upload.wikimedia.org/wikipedia/commons/9/94/Selection-Sort-Animation.gif)
+![Algorithm Visualization](https://upload.wikimedia.org/wikipedia/commons/9/94/Selection-Sort-Animation.gif)