[k8s] document differences and current limitations of stack deploy on k8s

[thaJeztah]

relates to #721

Docker 18.01 will ship with a preview/experimental support for deploying stacks on k8s. We should document the differences between deploying on SwarmKit, current limitations, and known issues. At least;

• how to enable k8s integration on Docker for Desktop
• how to use against an existing k8s cluster (is this currently possible?)
• limitations around deploying multiple stacks with a service that has the same name ([k8s] stacks should have their own namespace #776)
• limitations around re-deploying a stack that uses secrets (or configs); [k8s] updating a stack with secrets should detect that the secret didn't change #777
• a known issue with the --namespace option not working (or not fully working) for stacks
• that this preview only supports the docker stack commands, but other commands are not yet available.

[thaJeztah]

We can add a document in https://github.com/docker/cli/tree/master/experimental and link to that from the documentation

[motin]

Does these have separate tracking issues yet, or any documentation?

• how to use against an existing k8s cluster (is this currently possible?)
• a known issue with the --namespace option not working (or not fully working) for stacks
  The state of these limitations affect current decisions in our projects

[adeniyistephen]

@thaJeztah Hi,I would love to work on this, Please provide pointers and input on how to work on it. Thanks

[thaJeztah]

kubernetes integration was deprecated and removed; let me close this one