Add masquerade to etcd structure docs.
Add masquerade to etcd structure docs.

Former-commit-id: d50df882d03bb67980246c36af683f421b7d4a80
TrimBiggs/libnetwork-plugin,djosborne/libcalico,insequent/libcalico,alexhersh/libcalico,tomdee/libcalico,projectcalico/libcalico,plwhite/libcalico,caseydavenport/libcalico,Symmetric/libcalico,robbrockbank/libcalico,projectcalico/libnetwork-plugin,TrimBiggs/libnetwork-plugin,tomdee/libnetwork-plugin,L-MA/libcalico,TrimBiggs/libcalico