Merge remote-tracking branch 'upstream/master'
added user control parameters :centroid_indices and :on_empty to k_means
Remove extra whitespace & fix identation

All this patch does is remove trailing whitespace from the README file
and fix identation of the instructions. It's really simple, but I did
notice it while reading the project's code on GitHub -- which sucks. :(
Merge branch 'kmeans_on_empty'
Merge branch 'master' of https://github.com/coberlin/ai4r into coberlin-master