State the purpose of AC meetings

§ 3.2.4. Advisory Committee Meetings requires that AC meetings happen, but it doesn't concisely state why AC meetings are even a thing. Why do we require the Team to organize two AC meetings each year? @cwilso's comment on #1094 suggests a rationale:

One of the most important parts of this in-person interaction is the ability to have two-way conversations: having advisory committee meetings that are one way presentation focused is not a great use of time. […] Having the ability to meet and have interactive discussions across membership stakeholders on various topics is very important however.

I'm inclined to agree. I suspect something along these lines is a widely shared belief among the membership: the AC meeting is important because it provides an opportunity for the AC to have frank discussions on matters of import to it and to the consortium.

Perhaps the Process section on AC meetings would benefit from the addition of a one-sentence statement of purpose, along these lines.

Start with § 3.2.4, Advisory Committee Meetings, in the Process Document and review the linked discussion in issue #1094. Add a concise statement explaining the purpose of AC meetings, reflecting their role in frank, interactive discussions. Done means the section clearly states why the meetings are required.