Link to Astro docs for heading anchor link generation (#1010)

Co-authored-by: Elian ☕️ <[email protected]>
Co-authored-by: Chris Swithinbank <[email protected]>

docs/src/content/docs/guides/authoring-content.md

@@ -89,6 +89,7 @@ I can link to [my conclusion](#conclusion) lower on the same page.
 
 Level 2 (`<h2>`) and Level 3 (`<h3>`) headings will automatically appear in the page table of contents.
 
+Learn more about how Astro processes heading `id`s in [the Astro Documentation](https://docs.astro.build/en/guides/markdown-content/#heading-ids)
 ## Asides
 
 Asides (also known as “admonitions” or “callouts”) are useful for displaying secondary information alongside a page’s main content.