Solid CG Charter

I spotted an issue raised by Sarven about the Solid CG Charter (
https://github.com/solid/process/pull/323 ).

I propose that this, along with the WG formation, needs an extended group
review.

Some thoughts:

   - Key elements should be discussed via a mailing list.
   - Anyone interested in volunteering their time to help the CG, should
   say so
   - For a small group, voting should be used as a last resort, not a first
   step.
   - We need to clarify the Solid WG's role before deciding the CG's next
   steps.

Let's involve the whole group in deciding how we take the CG forward,
bearing in mind many will be on summer vacation, too