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 #37 from claco/contributing

Merged automatically by jenkins after successful build test
Pass username to get_user_home instead of hash

When admin_user is a hash, ensure we get the username and pass that to
get_user_home instead of passing the hash itself.
Merge pull request #38 from claco/fix-configurekeys-with-hash

Merged automatically by jenkins after successful build test
Updating version # to 4.1.2