Update link to KaTeX CSS in docs

[victor23k]

Closes GH-#2341

Remove old link to katex.css and refer to the katex docs to get the latest version.

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Name	Status	Preview	Comments	Updated (UTC)
mdx	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	Oct 9, 2023 4:58pm

[wooorm]

Can’t we have both? I think this new text is easy to miss.

[victor23k]

Hi @wooorm, I added back the link section with the katex version updated and also updated the modified date of the page. Thanks for the direction and looking forward to helping more 😄.

[wooorm]

Thank you!!