add section on semantic versioning
add section on semantic versioning

This documentation was ripped from the Helm v2.2.0 release notes. I've referenced it enough times that
it should be placed somewhere in the documentation.

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