Flannel steps are hard to skip, in our Kubernetes guide

[pgburt]

User reported an issue on our google groups here: https://groups.google.com/forum/#!topic/coreos-user/-dQ-fIyzV9g

They're receiving an error from Flannel, after attempting to skip the Flannel section of the guide. We should find a way to differentiate optional / forking paths in guides better. Right now they're fairly confusing.

cc @zbwright

[zbwright]

agreed. Thanks @pgburt.