Update: index.html: Add link to metrics

index.html

@@ -51,6 +51,7 @@
 
 <p><a href="https://opennars.github.io/javadoc/index.html">Javadoc</a>
 
+<p><a href="https://github.com/opennars/Metrics/tree/master/OpenNARS%20version%20performance%20graphs">Metrics</a>
 
       </section>
     </div>