- Tweak the documention of Kafka.Version provided
  as comments in the orderer.yaml.
- Update the Fabric documentation to provide better
  guidance on setting Kafka.Verion and on its impact
  after an upgrade.
- NOTE that Fabric would, in effect no longer have a
  'supported' version of Kafka. Also note that does
  not stop downstream projects, such as ibmblockchain,
  from declaring which versions of Kafka they support.

Change-Id: I4da50d1186dedd18618b637edeb757c8cbdd5f7c
Signed-off-by: Luis Sanchez <sanchezl@us.ibm.com>