Update docs to mention additional soft dependencies

[juniorsysadmin]

Update docs to mention soft dependencies that have recently been taken out of Puppet core, like yum_repo

[dhoppe]

@juniorsysadmin I am not sure if we need to update the docs:

• https://github.com/voxpupuli/puppet-nodejs#module-dependencies

[Dan33l]

Since spec_helper_acceptance.rb does not add any core and acceptance tests pass, IMO the README.md file is correctly written.