Warn if solo.rb exists
Ensure cookbook_path is an Array

It is common to specify it as a string if there is only one cookbook
directory.
Comment out encrypted_data_bag_secret from the generated knife.rb
Warn if the local paths are not found

Chef/Knife configuration for cookbook_path etc. defaults to system
paths. So unless the user has configured her knife.rb, the paths
don't normally exist.
Update the changelog
Update the readme