Add katex example with documentation (#69)

exampleSite/content/posts/theme-documentation-advanced.md

@@ -99,6 +99,30 @@ Giving users the freedom to add anything in the HTML via config.toml seemed like
   """
 ```
 
+### Katex
+
+Katex is a math typesetting library for the web which lets you write beautiful equations. To use it, add the javascript as mentioned in [their documentation](https://katex.org/docs/browser.html) in our `params.customHeadHTML`.
+
+```markdown
+[params]
+  customHeadHTML = """
+    <link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/katex@0.13.16/dist/katex.min.css" integrity="sha384-6LkG2wmY8FK9E0vU9OOr8UvLwsaqUg9SETfpq4uTCN1agNe8HRdE9ABlk+fVx6gZ" crossorigin="anonymous">
+
+    <!-- The loading of KaTeX is deferred to speed up page rendering -->
+    <script defer src="https://cdn.jsdelivr.net/npm/katex@0.13.16/dist/katex.min.js" integrity="sha384-31El76TwmbHj4rF9DyLsygbq6xoIobG0W+jqXim+a3dU9W53tdH3A/ngRPxOzzaB" crossorigin="anonymous"></script>
+
+    <!-- To automatically render math in text elements, include the auto-render extension: -->
+    <script defer src="https://cdn.jsdelivr.net/npm/katex@0.13.16/dist/contrib/auto-render.min.js" integrity="sha384-vZTG03m+2yp6N6BNi5iM4rW4oIwk5DfcNdFfxkk9ZWpDriOkXX8voJBFrAO7MpVl" crossorigin="anonymous"
+        onload="renderMathInElement(document.body);"></script>
+  """
+```
+
+> Note: Make sure you use the latest version of katex and use the correct script tags as described in [their documentation](https://katex.org/docs/browser.html)
+
+Then the equation `$$y_t = \beta_0 + \beta_1 x_t + \epsilon_t$$` would be displayed as:
+
+   $$y_t = \beta_0 + \beta_1 x_t + \epsilon_t$$
+
 ## Syntax Highlighting
 
 Hugo lets you choose the color scheme for the codeblocks. You can choose from the options here: https://xyproto.github.io/splash/docs/all.html