title: Trying to run Rcpp in R but unable to create makevars file
body: <p>There have previous discussions regarding the compiler in XCode and its relation to the Rcpp package. For instance, here <a href="https://stackoverflow.com/a/19550947/1786009">https://stackoverflow.com/a/19550947/1786009</a> 
  It seems that the answer is to create a Makevars file in the directory ~/.R/Makevars
  My question is simple, how do I find where the .R directory is?</p>