Clarify <a> vs <button> language in

[robdodson]

Describe the bug
See #1017

https://web.dev/use-semantic-html
The text in this article is a little unclear when to use an anchor or a button. We mention adding new content to the page is allowed if you're using an anchor, but we should be more specific and say if you're using an anchor to navigate within a SPA and you use routing to update the URL then you should use an anchor.