Tweak wording a bit on `renderComponent` note

docs/ref-01-top-level-api.md

@@ -88,8 +88,9 @@ If the optional callback is provided, it will be executed after the component is
 
 > Note:
 >
-> `React.renderComponent()` currently replaces the contents of the node.
-> This restriction may go away in the future.
+> `React.renderComponent()` replaces the contents of the container node you
+> pass in. In the future, it may be possible to insert a component to an
+> existing DOM node without overwriting the existing children.
 
 
 ### React.unmountComponentAtNode