Just download the appropriate binary for your OS, place rtelegram in your $PATH and you are good to go.
Or if you have Go installed: go get -u github.com/pyed/rtelegram
Thanks to pyed/rtapi You don't need a complicated webserver setup, All you need is:
rTorrentcompiled with the flag--with-xmlrpc-c. Which you probably already have.scgi_port = localhost:5000in yourrtorrent.rcfile.
And you should be good to go!