I'm not sure about points 3 and 4. Why we should advise to install 1.9.3 over 1.9.2 or 2.0.0 for instance? Some Linux distros also ship with a recent version Ruby (most of them have at least 1.9.2 which is the minimum required version). I would reword these two points like this.

* Set up Ruby on your machine. The minimum required version is 1.9.2 ; check the current one with `ruby -v`. Please rely on [RVM](http://rvm.io/) if your system can't get a recent version.