Some code samples need updating for best practice

Reading through https://guides.emberjs.com/release/components/template-lifecycle-dom-and-modifiers/

There are some code samples that could use an update, as they are out-of-date for best practices.

Specifically, the examples showing an `article` element containing a `header` and an `h1`.

These days, it's really best to have one `header` and one `h1` per page. It would be fine to change these to divs with demonstrative classes on them, e.g.,

```hbs