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 pull request #15 from agarie/minor_fixes_readme

Remove extra whitespace & fix identation
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'