Update link to KaTeX CSS in docs

Closes GH-2341.
Closes GH-2360.

Reviewed-by: Titus Wormer <tituswormer@gmail.com>

docs/guides/math.mdx

@@ -5,7 +5,7 @@ export const info = {
     {name: 'Titus Wormer', github: 'wooorm', twitter: 'wooorm'}
   ],
   published: new Date('2021-10-06'),
-  modified: new Date('2022-12-14')
+  modified: new Date('2023-10-09')
 }
 
 # Math
@@ -71,8 +71,10 @@ console.log(
   At the time of writing, the last version is:
 
   ```html
-  <link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/katex@0.15.2/dist/katex.min.css" integrity="sha384-RZU/ijkSsFbcmivfdRBQDtwuwVqK7GMOw6IMvKyeWL2K5UAlyp6WonmB8m7Jd0Hn" crossorigin="anonymous">
+  <link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/katex@0.16.9/dist/katex.min.css" integrity="sha384-n8MVd4RsNIU0tAv4ct0nTaAbDJwPJzDEaqSD1odI+WdtXRGWt2kTvGFasHpSy3SV" crossorigin="anonymous">
   ```
+
+  To get the latest link to the stylesheet, go to [`katex docs`][katex docs].
 </Note>
 
 <Note type="info">
@@ -95,3 +97,5 @@ console.log(
 [options-rehype-plugins]: /packages/mdx/#optionsrehypeplugins
 
 [extend]: /docs/extending-mdx/
+
+[katex docs]: https://katex.org/docs/browser#loading-as-global