Tweaks to CONTRIBUTING/README/etc following new naming convention

[benjie]

@graphql/gaps-editors please merge :)

I just went through and filed #13, I've updated the CONTRIBUTING, README, and structure validation to clarify any ambiguities around the new situation and to allow more progress at the time of filing the GAP. I've also created the @graphql/gaps-editors team 😁

[magicmark]

@benjie who will be in @graphql/gaps-editors? folks that care about maintaining gaps? or all folks who have ever submitted a GAP (and likely/may only care about their specific GAP)?

I'm assuming the former since Ping @graphql/gaps-editors to find a sponsor is great guidance, I was thinking of adding something along the same lines - but then "editors" is maybe overloaded. Maybe @graphql/gaps-sponsors?

[benjie]

gaps-editors are people who have "Write" access to this repo - they can merge PRs, etc. They'll essentially be people approved by the TSC to run the program. Currently it's Martin, you and me but we can add others as volunteers raise their hand and TSC approves.