Link to OPNFV docs for "what to do with ODL" examples

The docs include lots of info about installing ODL, ODL features and such. We don't have good examples of what to do with ODL once you have it. We used to be able to do this with smallish L2Swith demos and such, but now the uses are too complex to maintain ourselves.

OPNFV has tons of scenarios that use ODL, running code deployments of them in CI and easy ways to deploy them yourself. They also have good docs about these. Should just curate a set of links to those.