clarify why func components don't appear in devtools

Author: chrisvfritz

src/v2/guide/render-function.md

@@ -482,9 +482,9 @@ Everything the component needs is passed through `context`, which is an object c
 
 After adding `functional: true`, updating the render function of our anchored heading component would simply require adding the `context` argument, updating `this.$slots.default` to `context.children`, then updating `this.level` to `context.props.level`.
 
-Since functional components are just functions, they're much cheaper to render. However, this also mean that functional components don't show up in the [Vue devtools](https://github.com/vuejs/vue-devtools) component tree.
+Since functional components are just functions, they're much cheaper to render. However, the lack of a persistent instance means they won't show up in the [Vue devtools](https://github.com/vuejs/vue-devtools) component tree.
 
-They're also very useful as wrapper components.  For example, when you need to:
+They're also very useful as wrapper components. For example, when you need to:
 
 - Programmatically choose one of several other components to delegate to
 - Manipulate children, props, or data before passing them on to a child component