Add contribution guidance

Add CONTRIBUTING.md that points to the same document in chef-cookbooks
Add mention of the contribution document in the top of the README.md
Merge pull request #119 from claco/contributing

Merged automatically by jenkins after successful build test
Offline compression enable by default on RHEL packages. Changing to be consistent with Ubuntu.
Merge pull request #120 from git-harry/master

Merged automatically by jenkins after successful build test