Clarify that Quarto is successor to rmarkdown (and X-compatible)

[NeuroShepherd]

Small fix, but the note in

code-publishing/index.qmd

Line 22 in 716b4e0

Quarto is a tool to render dynamic documents, but not the only one. You may also use [`rmarkdown`](https://rmarkdown.rstudio.com/), [Jupyter Book](https://jupyterbook.org/), [Stencila](https://stencila.io/), [Curvenote](https://curvenote.dev/), [showyourwork!](https://show-your.work/), [Org Mode](https://orgmode.org/), [StatTag](https://sites.northwestern.edu/stattag/), or one of the countless others.

says that RMarkdown is an alternative.

Posit is no longer doing active development on RMarkdown in favor of using Quarto, and users should actively move to Quarto. I would provide this history, and also let people know that Quarto can still render their .Rmd, .md, and I think .ipynb files.

[fkohrt]

I tried to cover this via 2f0747b

[NeuroShepherd]

Perfect!