Merge pull request #253 from opscode/sh/upgrade-errata

touch up new upgrade notes
updates for chef-client 11-12 release

need to add bug list to 11-12 release notes
sync up release notes/index
clone release notes from master
no _
add changelog

temporary until bullet list can be added
fix typo; sync OPERATORS
add disabling plugins to release notes
Make upgrade docs more generic to cover OPC 1.4.6+ and EC11.1.x