Hello. I need to install Rtools in order to work with keras package. I've successfully downloaded Rtools from https://cran.r-project.org/bin/windows/Rtools/, but then I need to "put it on a path", as it is stated here on this website. I don't understand what is written here about doing that. Could you,please, explain it to me in a simple way and, desirably, with an example?