docs/developers.md: add notes for `k8s.io` dir
docs/developers.md: add notes for `k8s.io` dir

technosophos/deployment-manager,michelleN/deployment-manager,adamreese/helm,appscode/helm,adamreese/deployment-manager,appscode/helm,technosophos/deployment-manager,technosophos/k8s-helm,technosophos/k8s-helm,fibonacci1729/helm,michelleN/deployment-manager,technosophos/deployment-manager,adamreese/helm,michelleN/deployment-manager,adamreese/deployment-manager,SlickNik/helm,adamreese/deployment-manager,bacongobbler/helm,technosophos/deployment-manager,helm/helm,jascott1/helm,adamreese/deployment-manager,eicnix/helm,michelleN/deployment-manager,bacongobbler/helm,adamreese/deployment-manager,technosophos/deployment-manager,eicnix/helm,jascott1/helm,helm/helm,fibonacci1729/helm,SlickNik/helm