Document support for UDP.
Document support for UDP.

[#84379694]

Signed-off-by: Steve Powell <03c892efa7d90f6161831192fc2bb1ab9ff2d4d9@pivotal.io>

savaki/garden,cloudfoundry-incubator/garden,savaki/garden,cloudfoundry-incubator/garden,tangfeixiong/garden,tangfeixiong/garden