Update documentation for CMDSTANR_USE_MSYS_TOOLCHAIN

DESCRIPTION

@@ -32,7 +32,7 @@ URL: https://mc-stan.org/cmdstanr/, https://discourse.mc-stan.org
 BugReports: https://github.com/stan-dev/cmdstanr/issues
 Encoding: UTF-8
 LazyData: true
-RoxygenNote: 7.3.1
+RoxygenNote: 7.3.2
 Roxygen: list(markdown = TRUE, r6 = FALSE)
 SystemRequirements: CmdStan (https://mc-stan.org/users/interfaces/cmdstan)
 Depends:

R/install.R

@@ -20,8 +20,19 @@
 #'
 #'   The `check_cmdstan_toolchain()` function attempts to check for the required
 #'   C++ toolchain. It is called internally by `install_cmdstan()` but can also
-#'   be called directly by the user.
+#'   be called directly by the user. On Windows only, calling the function with
+#'   the `fix = TRUE` argument will attempt to install the necessary toolchain
+#'   components if they are not found. For Windows users with RTools44 no additional
+#'   toolchain configuration is required. For users with older versions of RTools,
+#'   the function will install `mingw32-make` and `g++` from MSYS using the
+#'   RTools-provided `pacman` package manager. This can also be manually requested
+#'   by setting the environment variable `CMDSTANR_USE_MSYS_TOOLCHAIN` to 'true'
 #'
+#'   NOTE: When installing CmdStan on Windows with RTools44 and CmdStan versions
+#'   prior to 2.35.0, the above additional toolchain configuration
+#'   is still required. To enable this configuration, set the environment variable
+#'   `CMDSTANR_USE_MSYS_TOOLCHAIN` to 'true' and call
+#'   `check_cmdstan_toolchain(fix = TRUE)`.
 #'
 #' @export
 #' @param dir (string) The path to the directory in which to install CmdStan.