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 #34 from claco/contributing

Merged automatically by jenkins after successful build test
add default param for db attribute
Merge pull request #35 from jrcloud/de278-mysql-collectd-dupes

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