Groups TF update

At our last CG meeting, we agreed to create a Groups task force. The TF 
now has a repository:

https://github.com/swicg/groups

a and I have been added as committers on the repo.

We've got an initial set of user stories for groups:

https://github.com/swicg/groups/issues?q=is%3Aissue+is%3Aopen+label%3A%22user+story%22

a and I discussed having a TF meeting this month, and we decided that it 
might make more sense to work asynchronously for now, and consider a 
meeting afterwards.

I think the next big question for the TF is what the scope would be. I 
suggested potentially these deliverables:

  * A Report on how to use Activity Streams 2.0 and ActivityPub to
    implement group functionality, possibly including new vocabulary
    terms like /members/.
  * A reference implementation of groups.
  * Testing tools for Groups implementations.

Evan