Found an inconsistency in Lab 21

In this autodidactic course to learn the basics of git, it is never separately said that you need the packages (if you use Linux) `ruby` and `rubygems`.
 But in Lab 21 you need the 'rake' gem, it would be better, if you tell the user to enter `gem install rake` in the terminal, before they go on with learning and before they test their `rakefile`. 
If somebody is a newcomer to both ruby and git like me, he might get quite confused by these necessary extra steps.