make sure we don't break docs when we merge changes to master

[errordeveloper]

When #460 got merged, we broke the config file samples in the examples and in README.md. We need to get better at this and only update docs when release is ready to use.

[mumoshu]

My quick idea towards this is add eksctl a command to validate a config file, like eksctl create cluster --config-file 01-simple-cluster.yaml --dry-run, so that it can be used to validate syntactic correctness of all the examples in CI.

[errordeveloper]

@mumoshu I think we need --dry-run anyway, but I'm not entirely sure what the output would look like (let's discuss in #476). I was more thinking about versioning the docs. We might have outgrown the current website also, which presets just what's in the readme. Something to think about, not urgent just yet - for now we just need to be careful about when we merge documentation changes.