Add various improvements

[martialblog]

Hello,

I've added some stuff:

• Update metadata to ensure puppetlabs-stdlib 5.* is a dependency

The setting was < 5.0.0, but the stdlib is at 5.2.0 currently. Now the warning is gone and the installation runs without issues.

• Add checksum parameter for puppet-archive

This ensures the integrity of the package and addresses malicious tampering. I also updated to 1.7.5, which required an extra parameter (release), since the download URL is:

https://storage.googleapis.com/harbor-releases/release-1.7.0/harbor-offline-installer-v1.7.5.tgz

• Add support for Debian 9 Stretch

By adding puppetlabs-apt and updating the exec resource. Tested that in Vagrant, works like a charm :whale:

• Add some more documentation to the parameters; Update README and add CONTRIBUTING.md

You can drop these is you want, just thought it might be nice to have.

Cheers, Markus

[walkamongus]

awesome -- thanks @martialblog!