Added slot to todo list component (#763)

* Added slot to todo list component

Added slot to todo list component to emphasize the fact that you can replace the content with custom content.
As the sentence states, this won't work without scoped slots.

* fix: changed wording on slot

Co-authored-by: Natalia Tepluhina <[email protected]>

Author: hitautodestruct

src/guide/component-slots.md

@@ -247,7 +247,7 @@ app.component('todo-list', {
 })
 ```
 
-We might want to replace the slot to customize it on parent component:
+We might want to replace the `{{ item }}` with a `<slot>` to customize it on parent component:
 
 ```html
 <todo-list>