clarifies the puppet-strings usage

This is part of the OpenVox rebranding. This summary string is part of
the `puppet --help` output.

Author: binford2k

lib/puppet/face/strings.rb

@@ -4,7 +4,7 @@
 
 # Implements the 'puppet strings' interface.
 Puppet::Face.define(:strings, '0.0.1') do # rubocop:disable Metrics/BlockLength
-  summary 'Generate Puppet documentation with YARD.'
+  summary 'Generate Puppet module documentation with YARD.'
 
   action(:generate) do
     default