Flesh out example in README
Flesh out example in README

I'm reluctant to give exhaustive details of the available options in the
README since they are well documented in the class using `puppetdoc` format.
Duplicating is likely to lead to one or the other being badly maintained.

I really wish there was a nice mechanism for rendiner `puppetdoc` to GitHub
or Forge READMEs.

gds-operations/puppet-resolvconf,gds-operations/puppet-resolvconf