docs: fix typo in syntax.md (#171)

Author: stefanfreitag

guide/syntax.md

@@ -646,9 +646,9 @@ src: ./content.md
 
 > Available since v0.43.0
 
-Slidev has and experimental support for [MDC (Markdown Components) Syntax](https://content.nuxtjs.org/guide/writing/mdc) powered by [`markdown-it-mdc`](https://github.com/antfu/markdown-it-mdc).
+Slidev has an experimental support for [MDC (Markdown Components) Syntax](https://content.nuxtjs.org/guide/writing/mdc) powered by [`markdown-it-mdc`](https://github.com/antfu/markdown-it-mdc).
 
-You can enable it by add `mdc: true` to the frontmatter of your markdown file.
+You can enable it by adding `mdc: true` to the frontmatter of your markdown file.
 
 ```md
 ---