Clarify effect of ‘only’ language (#2264)

Clarify that ‘only’ does not preclude `<Content />` from rendering.

content/docs/jsx-in-depth.md

@@ -423,7 +423,7 @@ Children passed to a custom component can be anything, as long as that component
 <div>{true}</div>
 ```
 
-This can be useful to conditionally render React elements. This JSX only renders a `<Header />` if `showHeader` is `true`:
+This can be useful to conditionally render React elements. This JSX renders the `<Header />` component only if `showHeader` is `true`:
 
 ```js{2}
 <div>