Maintaining GitHub alert syntax in README with devtools::build_readme()

[jhelvy]

I usually build the README.md file in my R packages with devtools::build_readme() from a README.Rmd file.

I use GitHub alerts like these in some of my README.Rmd files, but the alert syntax is not preserved after rendering. Here are two examples:

This README.Rmd:

---
output: github_document
---

> [!NOTE]
> A note

Renders to:

> \[!NOTE\] A note

Note how the brackets are escaped, which breaks the alert syntax.

I have also tried to maintain the syntax by placing this inside a markdown chunk, like this:

---
output: github_document
---

```{markdown}
> [!NOTE]
> A note
```

But this then renders with the markdown chunk still in place:

```{markdown}
> [!NOTE]
> A note
```

So this also doesn't work.

I'm not sure if this is an issue with devtools, knitr, or something else. I suspect it may be how knitr handles github documents, but I figured I would post the issue here first in case something is happening internally with devtools::build_readme()