add support latex to papermod theme.

Signed-off-by: lijiansheng <lijiansheng@opensourceway.community>

Author: lijiangsheng1

layouts/_partials/extend_head.html

@@ -0,0 +1,15 @@
+<!-- KaTeX support for LaTeX math rendering -->
+<link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/katex@0.16.11/dist/katex.min.css" integrity="sha384-nB0miv6/jRmo5UMMR1wu3Gz6NLsoTkbqJghGIsx//Rl+OelDp16Cj4b04MmijT8" crossorigin="anonymous">
+<script defer src="https://cdn.jsdelivr.net/npm/katex@0.16.11/dist/katex.min.js" integrity="sha384-7zkQWkzuo3B5wH2C0u2i2R2wY2Lvy0Vi5KFr5XCCD86hSX2CBfIG2j0IpCkOY2UTc" crossorigin="anonymous"></script>
+<script defer src="https://cdn.jsdelivr.net/npm/katex@0.16.11/dist/contrib/auto-render.min.js" integrity="sha384-43gviWU0YVjaDtb/GhzOoOXtS0s9eQp3Pp7OprMpP1eHOnG2oHGFiKUpMiAlLt" crossorigin="anonymous"></script>
+<script>
+  document.addEventListener("DOMContentLoaded", function() {
+    renderMathInElement(document.body, {
+      delimiters: [
+        {left: "$$", right: "$$", display: true},
+        {left: "$", right: "$", display: false}
+      ],
+      throwOnError: false
+    });
+  });
+</script>