[docs] Mention yarn pretty (#2103)

docs/README.md

@@ -44,7 +44,8 @@ yarn dev
 For an editor, VSCode is a good choice. Also install the Prettier extension for
 VSCode, and set VSCode to format on save. This way the editor will automatically
 format and wrap the text using the project's standard, so you can just focus on
-the content.
+the content. You can also format without VSCode by using the `yarn pretty`
+command.
 
 ## Have fun!