Update README with getvar() and validate_hash()
Update README with getvar() and validate_hash()

The README now provides quick examples of how to take advantage of the
getvar() and validate_hash() functions included in this release of the
stdlib.

jbondpdx/puppetlabs-stdlib,yadavnikhil/puppetlabs-stdlib,puppetlabs/puppetlabs-stdlib,HelenCampbell/puppetlabs-stdlib,fuel-infra/puppetlabs-stdlib,DavidS/puppetlabs-stdlib