Fix grammar on the Getting Started page (WordPress#51661)

Author: Sidsector9

docs/getting-started/README.md

@@ -20,7 +20,7 @@ Welcome! Let's get started building with blocks. Blocks are at the core of exten
 -   Learn [about using theme.json](/docs/how-to-guides/themes/theme-json.md) to define settings and styles for your theme.
 
 -   [Create a Block Theme](/docs/how-to-guides/themes/create-block-theme.md) - Learn how block themes use blocks to build templates and the theme.json to provide styles.
--   [Convert as Classic Theme to a Block Theme](https://developer.wordpress.org/themes/block-themes/converting-a-classic-theme-to-a-block-theme/) - Learn how to adopt various pieces of full site editing in your classic theme.
+-   [Convert a Classic Theme to a Block Theme](https://developer.wordpress.org/themes/block-themes/converting-a-classic-theme-to-a-block-theme/) - Learn how to adopt various pieces of full site editing in your classic theme.
 
 ## Ways to Stay Informed