Now that we are starting to get backlog specs, make it clear how one can
take it over and implement it.
* Make it clear on the landing page that backlog specs are looking for
owners. Hopefully this will guide developers looking for a spec to
work in to the right place.
* Explain how to take over a backlog spec.
Change-Id: Ia3585c515c115e073c00e3222fc6718da79792b9
54a0cc035b