add example site

exampleSite/layouts/partials/foot_custom.html

@@ -0,0 +1,12 @@
+<script src="https://yihui.name/js/math-code.js"></script>
+<script type="text/x-mathjax-config">
+MathJax.Hub.Config({
+  tex2jax: {
+    inlineMath: [['$','$'], ['\\(','\\)']],
+    processEscapes: true
+  }
+});
+</script>
+<script async src="//cdn.bootcss.com/mathjax/2.7.1/MathJax.js?config=TeX-MML-AM_CHTML"></script>
+
+<script async src="https://yihui.name/js/center-img.js"></script>