feat: add TeX mhchem extensions for MathJax

Signed-off-by: Max Wu <[email protected]>

Author: jackycute

public/js/mathjax-config-extra.js

@@ -4,5 +4,8 @@ window.MathJax = {
   tex2jax: {
     inlineMath: [['$', '$'], ['\\(', '\\)']],
     processEscapes: true
+  },
+  TeX: {
+    extensions: ['mhchem.js']
   }
 }