Add API doc for security groups endpoint
Add API doc for security groups endpoint

Signed-off-by: Maria Shaldybin <a39f51a90bfcf8ca23756ef12127e1cf20796cba@vmware.com>

cloudfoundry-incubator/cf-networking-release,cloudfoundry-incubator/cf-networking-release,cloudfoundry-incubator/cf-networking-release,cloudfoundry-incubator/cf-networking-release