To get rErlang running and install R, follow these instructions:
Run install.sh with sudo rights, this will download and install R.
$ sudo install.sh
Now you need to install the forecast package in R. This is done by starting R using the command 'R' and running the function 'install.packages'. You may be prompted with a question, just press 'Y'.
$ R
> install.packages("forecast")
> q()
$
Now you are ready to compile rErlang! Write 'make'!
$ make
After this step, you are done! Yay!