edit: add smartypants to Markdown defaults

src/pages/en/guides/markdown-content.mdx

@@ -422,7 +422,7 @@ Custom components defined and exported in an MDX file must be imported and then
 
 Markdown support in Astro is powered by [remark](https://remark.js.org/), a powerful parsing and processing tool with an active ecosystem. Other Markdown parsers like Pandoc and markdown-it are not currently supported.
 
-Astro applies the [GitHub-flavored Markdown](https://github.com/remarkjs/remark-gfm) plugin by default. This brings some niceties like generating clickable links from text.
+Astro applies the [GitHub-flavored Markdown](https://github.com/remarkjs/remark-gfm) and [SmartyPants](https://github.com/silvenon/remark-smartypants) plugins by default. This brings some niceties like generating clickable links from text, and formatting for [quotations and em-dashes](https://daringfireball.net/projects/smartypants/).
 
 You can customize how remark parses your Markdown in `astro.config.mjs`. See the full list of [Markdown configuration options](/en/reference/configuration-reference/#markdown-options).