The example in README.md requires the ranger library, but this is not mentioned

[martinmodrak]

This is a minor thing, but following the installation instructions and running the demo, I get a bunch of errors like:

Loading required namespace: ranger
Failed with error:  ‘there is no package called ‘ranger’’
Error : loading required package (ranger) failed
Loading required namespace: ranger
Failed with error:  ‘there is no package called ‘ranger’’
In addition: Warning message:
In FUN(X[[i]], ...) : Error in algorithm m_ranger 
  The Algorithm will be removed from the Super Learner (i.e. given weight 0) 

The example works even without ranger, but it probably should instruct the users to install the ranger library (or avoid using it).

[martinmodrak]

Thanks!