I am trying to install Ruby on Rails. and i have followed the following link for the install https://www.digitalocean.com/community/articles/how-to-install-ruby-on-rails-on-ubuntu-12-04-lts-precise-pangolin-with-rvm. This link was helpful i was able to run it, and everything, however as soon has i restarted the computer i then go into my apps and run it again with rails s and this message occurs.

The program 'rails' is currently not installed.  You can install it by typing:
sudo apt-get install rails

But work before, what should i do, do i need to set the path of somesort?? I am not that great in linux so bear with me. I am using linux ubuntu 12.04 desktop and my user is john

Thanks in advance