Capitalize the word Markdown throughout the documentation

Closes #2435

content/en/functions/transform/Markdownify.md

@@ -1,6 +1,6 @@
 ---
 title: transform.Markdownify
-description: Renders markdown to HTML.
+description: Renders Markdown to HTML.
 categories: []
 keywords: []
 action:
@@ -24,8 +24,8 @@ To keep the wrapping `p` tags for a single paragraph, use the [`RenderString`] m
 [`RenderString`]: /methods/page/renderstring/
 
 {{% note %}}
-Although the `markdownify` function honors [markdown render hooks] when rendering markdown to HTML, use the `RenderString` method instead of `markdownify` if a render hook accesses `.Page` context. See issue [#9692] for details.
+Although the `markdownify` function honors [Markdown render hooks] when rendering Markdown to HTML, use the `RenderString` method instead of `markdownify` if a render hook accesses `.Page` context. See issue [#9692] for details.
 
-[markdown render hooks]: /render-hooks/
+[Markdown render hooks]: /render-hooks/
 [#9692]: https://github.com/gohugoio/hugo/issues/9692
 {{% /note %}}