Add 'contributors.md' and 'gettingstarted.md' pages

[postphotos]

We should give directions to those looking to dive in here.

[wordpress-privacy-archive]

What would go in the 'Getting Started' ? Probably the README.md (so the basic file opened when getting to https://github.com/gdpr-compliance/info) should contain the info on Getting Started (then pointing to other docs probably), or are you referring to other things?