Document what Sid said about the reason / when to start a working group

Why is this change being made?

The handbook has a discussion video which contains key information. This should be documented as text for easier discoverability and more efficient understanding of the role of working groups.

Verbatim, what Sid says is:

[You'd start one] when working asynchronous is too slow. A working group is expensive, you're gonna have meetings with busy people. So you only want to do it for important things. But some important things can be done asynchronous. But asynchronous tends to take more time than synchronous. So if you have an important problem that needs to be solved fast, you'd start a working group for it.

I've boiled that down, but we could just have the whole statement.

Author Checklist

• Provided a concise title for this Merge Request (MR)
• Added a description to this MR explaining the reasons for the proposed change, per say why, not just what
  • Copy/paste the Slack conversation to document it for later, or upload screenshots. Verify that no confidential data is added, and the content is SAFE
• Assign reviewers for this MR to the correct Directly Responsible Individual/s (DRI)
  • If the DRI for the page/s being updated isn’t immediately clear, then assign it to one of the people listed in the Maintained by section on the page being edited
  • If your manager does not have merge rights, please ask someone to merge it AFTER it has been approved by your manager in #mr-buddies
  • The when to get approval handbook section explains the workflow in more detail
• If the changes affect team members, or warrant an announcement in another way, please consider posting an update in #whats-happening-at-gitlab linking to this MR
  • If this is a change that directly impacts the majority of global team members, it should be a candidate for #company-fyi. Please work with internal communications and check the handbook for examples.

---