update rstudio doc according to #131

_posts/2012-02-02-rstudio.md

@@ -7,4 +7,6 @@ category: demo
 
 It is still too early for general users to read this page, but one thing for sure is that **knitr** will be supported in RStudio. For those who do not care about the risk of trying a development version, you can download a latest [daily build](http://www.rstudio.org/download/daily/) and enjoy the one-click PDF compilation in RStudio through **knitr**.
 
+You are free to choose different engines to knit or weave the document, such as `Sweave`, `knitr` or `pgfSweave`, and you can also use different LaTeX backends such as `pdflatex` or `xelatex`.
+
 Repeat: this is the development version, and general users should wait for a stable release.