New policy files for Chef CLient.

CHANGELOG.md: One line description of the changes.
RELEASE_NOTES.md: Important changes and breaking changes that needs to be called out in more detail in Release Notes.
DOC_CHANGES.md: Required doc changes in chef-docs.
CONTRIBUTIONS.md: One line description of the contributions with contributor info.
Opscode->Chef, typos, grammar
Add Chef Client MVPs
Minor sentence update.
Merge pull request #1285 from opscode/new-policy-files

New policy files for Chef Client.