Fix typo and formatting in etcdStructure.md
Fix typo and formatting in etcdStructure.md

Fix a typo in the name of an etcd key. Also, GitHub only renders an indented block as code if it’s preceded by an empty line; add the newline  to ensure it renders correctly.
robbrockbank/calico-docker,projectcalico/calico-docker,Metaswitch/calico-docker,projectcalico/calico-containers,caseydavenport/calico-containers,caseydavenport/calico-containers,robbrockbank/calico-docker,quater/calico-containers,insequent/calico-docker,robbrockbank/calico-containers,tomdee/calico-containers,robbrockbank/calicoctl,TrimBiggs/calico-containers,robbrockbank/calicoctl,robbrockbank/calico-containers,alexhersh/calico-docker,tomdee/calico-docker,Metaswitch/calico-docker,projectcalico/calico-containers,caseydavenport/calico-docker,caseydavenport/calico-containers,TrimBiggs/calico-docker,quater/calico-containers,alexhersh/calico-docker,tomdee/calico-containers,projectcalico/calico-docker,projectcalico/calico-containers,TrimBiggs/calico-docker,caseydavenport/calico-docker,insequent/calico-docker,TrimBiggs/calico-containers,tomdee/calico-docker