Improve R install docs (#22737)

Release Notes:

- N/A

docs/src/languages/r.md

@@ -7,15 +7,54 @@ R support is available through the [R extension](https://github.com/ocsmit/zed-r
 
 ## Installation
 
-- [Install R](https://cloud.r-project.org/)
+1. [Download and Install R](https://cloud.r-project.org/).
-- Install the R packages `languageserver` and `lintr`:
+2. Install the R packages `languageserver` and `lintr`:
 
 ```R
 install.packages("languageserver")
 install.packages("lintr")
 ```
 
-- Install the [R extension](https://github.com/ocsmit/zed-r) through Zed's extensions
+3. Install the [R Zed extension](https://github.com/ocsmit/zed-r) through Zed's extensions manager.
+
+For example on macOS:
+
+```sh
+brew install --cask r
+Rscript --version
+Rscript -e 'options(repos = "https://cran.rstudio.com/"); install.packages("languageserver")'
+Rscript -e 'options(repos = "https://cran.rstudio.com/"); install.packages("lintr")'
+Rscript -e 'packageVersion("languageserver")'
+Rscript -e 'packageVersion("lintr")'
+```
+
+## Ark Installation
+
+To use the Zed REPL with R you need to install [Ark](https://github.com/posit-dev/ark), an R Kernel for Jupyter applications.
+You can down the latest version from the [Ark GitHub Releases](https://github.com/posit-dev/ark/releases) and then extract the `ark` binary to a directory in your `PATH`.
+
+For example to install the latest non-debug build:
+
+```sh
+# macOS
+cd /tmp
+curl -L -o ark-latest-darwin.zip \
+    $(curl -s "https://api.github.com/repos/posit-dev/ark/releases/latest" | \
+    jq -r '.assets[] | select(.name | contains("darwin-universal") and (contains("debug") | not)) | .browser_download_url')
+unzip ark-latest-darwin.zip ark
+sudo mv /tmp/ark /usr/local/bin/
+```
+
+```sh
+# Linux X86_64
+cd /tmp
+curl -L -o ark-latest-linux.zip \
+    $(curl -s "https://api.github.com/repos/posit-dev/ark/releases/latest" \
+        | jq -r '.assets[] | select(.name | contains("linux-x64") and (contains("debug") | not)) | .browser_download_url'
+    )
+unzip ark-latest-linux.zip ark
+sudo mv /tmp/ark /usr/local/bin/
+```
 
 <!--
 TBD: R REPL Docs