This package isn't on CRAN yet, but you can install it from this repository using the devtools
package,
devtools::install_github("stencila/r")
Alternatively, check the releases page for prebuilt versions.
Then install the package so that other Stencila packages and applications can detect it:
stencila:::install()
This package lets you run R code from inside Stencila Documents. When you start the Stencila Desktop it will be automatically detect the installed R package and you'll be able to execute R code cells from within your documents.