added mention of rstudio-prefs.json

cs50.dev.md

@@ -44,6 +44,7 @@ If using Firefox, [disable Enhanced Tracking Protection](https://support.mozilla
 * Visit [cs50.dev/commits](https://cs50.dev/commits) to access all of the commits that have been pushed to your repository in CS50's GitHub organization.
 * Visit [cs50.dev/repo](https://cs50.dev/repo) to access your repository in CS50's GitHub organization.
 * Visit [cs50.dev/restart](https://cs50.dev/restart) to restart your codespace.
+* Visit [cs50.dev/rstudio-prefs.json](https://cs50.dev/rstudio-prefs.json) for the latest version of CS50's RStudio preferences.
 * Visit [cs50.dev/settings.json](https://cs50.dev/settings.json) for CS50's default settings for VS Code.
 * Visit [cs50.dev/stop](https://cs50.dev/stop) to stop your codespace.
 * Visit [cs50.dev/update50.sh](https://cs50.dev/update50.sh) for the latest version of `update50`.