consistent language in "root-level layouts" section (#748)

Author: rpivo

src/routes/solid-router/concepts/layouts.mdx

@@ -8,7 +8,7 @@ Layouts are components that wrap the content of a route and can be used to defin
 ## Root-level layouts
 
 A root-level layout acts as a container surrounding all routes within your application.
-To define a route-level layout, pass the layout component to the `root` prop of the `Router` component:
+To define a root-level layout, pass the layout component to the `root` prop of the `Router` component:
 
 ```jsx
 import { render } from "solid-js/web";