added powered by for mathjax

index.html

@@ -122,6 +122,9 @@
             <a href="https://github.com/simonwhitaker/github-fork-ribbon-css">
                 <button class="indent">simonwhitaker/github-fork-ribbon-css</button>
             </a>
+            <a href="https://github.com/mathjax/MathJax">
+                <button class="indent">mathjax/MathJax</button>
+            </a>
         </div>
     </div>
     <a class="github-fork-ribbon left-bottom" href="http://github.com/parkjs814/AlgorithmVisualizer"