add a README.md for module diamond

it's nice to have one in each module

but not really doing the whole TOC thing
http://docs.puppetlabs.com/puppet/latest/reference/modules_documentation.html#readme-template

if we _really_ wanted to:
http://docs.puppetlabs.com/puppet/latest/reference/READMEtemplate.markdown

.md for markdown
http://daringfireball.net/projects/markdown/syntax

Change-Id: I944db7a0b6661bf4e9341004700755755a39e1ea