Update README.md

Author: bdcoder2

README.md

@@ -6,8 +6,9 @@
 <ul>
   <li><a href="https://bdcoder2.github.io/grid_clusterer/ex1/index.html">Creating data points vs creating Google map markers</a></li>
   <li><a href="https://bdcoder2.github.io/grid_clusterer/ex0/index.html">Tiles and grid points</a></li>
-  <li><a href="https://bdcoder2.github.io/grid_clusterer/ex2/index.html">Clusterer configuration options and performance</a></li>
+  <li><a href="https://bdcoder2.github.io/grid_clusterer/ex2/index.html">Clusterer configuration options and performance (using &quot;Classic&quot; markers)</a></li>
   <li><a href="https://bdcoder2.github.io/grid_clusterer/ex3/index.html">Enabling and disabling cluster marker click checks</a></li>
+  <li><a href="https://bdcoder2.github.io/grid_clusterer/ex4/index.html">Clusterer configuration options and performance (using &quot;Advanced&quot; markers)</a></li>
   <li><a href="https://bdcoder2.github.io/grid_clusterer/reference.html">Clusterer Reference</a></li>
 </ul>
 <p>