doc: Add CHANGELOG and UPGRADING docs

doc: Add CHANGELOG and UPGRADING docs

The CHANGELOG document should describe the high level changes of the
project. This will provide a human-readable way for people to evaluate
the changes in each release. This file is based on the templates and
general changelog "ethos" provided by 'Keep a CHANGELOG':

    http://keepachangelog.com/

The UPGRADING document provide instruction for system admininstrators
managing patchwork deployments. At the moment, this document is a
rename and minor reformatting of the existing 'docs/NEWS' document, but
going forward documentation will be added for each new release.

Signed-off-by: Stephen Finucane <stephen.finucane@intel.com>