Add contributing and testing docs

This will increase our cookbook quality score on supermarket

Signed-off-by: Tim Smith <tsmith@chef.io>

CONTRIBUTING.md

+# Contributing
+
+## Branches
+
+### `master` branch
+
+The master branch is the current committed changes. These changes may not yet be released although we try to release often.
+
+## Tags
+
+All releases are tagged in git. To see the releases available to you see the changelog or the tags directly.
+
+
+## Pull requests
+
+- <https://github.com/bmhatfield/chef-ulimit/pulls>
+
+## Issues
+
+Need to report an issue? Use the github issues:
+
+- <https://github.com/bmhatfield/chef-ulimit/issues>

TESTING.md

+Please refer to
+https://github.com/chef-cookbooks/community_cookbook_documentation/blob/master/TESTING.MD