Update README.md

README.md

@@ -59,7 +59,7 @@ console and type `R` in there). The default choice of R DE on
 Steps:
 
 1. Fire up emacs
-2. `Alt-x` and `R` gets you an R session
+2. `Alt-x` (`Cmd-x` for Mac) and `R` gets you an R session
 3. If asked, set your start working directory, e.g. 
 `setwd('/mnt/scratch/user/')` 
 (where `user` is an alias for your username)