Thanks for asking and we don't have this built into the product as R does. However, you can simply use standard APA, MLA or other formatting standards.
Version: (whatever you downloaded)
City: Boston, MA
Retrieval Date: (when you downloaded RStudio)
RStudio (2012). RStudio: Integrated development environment for R (Version 0.96.122) [Computer software]. Boston, MA. Retrieved May 20, 2012.
Available from http://www.rstudio.org/