feat: Qmd example similar to documentation

[coatless]

Port of the .Rmd over to .qmd. Lacks the grand styling touch.

We also moved the existing example.qmd over to template.qmd that will be available if the extension is installed using:

quarto use template gadenbuie/countdown/quarto

Instead of:

quarto add gadenbuie/countdown/quarto

Useful links:

• https://emitanaka.org/blog/2022-07-11-transitioning-from-xaringan-to-quarto-revealjs/transitioning-from-xaringan-to-quarto-revealjs.html
• https://quarto.org/docs/presentations/revealjs/

Close #48

[coatless]

@gadenbuie Okidokie, this is ready for a review/stylistic touch. Content-wise, it matches decently with the .Rmd; however, there is no theme to the example deck.

A quick "TODO" left would be to understand if it's possible to "capture" the short code output and display it as HTML. Don't get your hopes up on this; we'll likely need to do a copy + paste of the generated HTML.