docs: Add Guide to Leading a Coffee Table Group

[meg-gutshall]

Summary

Context

I think we need some general documentation around what is expected of a Coffee Table Group Lead and how this role has separate responsibilities from Coffee Table Group Host (though one can have both roles). We have something posted on the website, but it's out of date.

Goals

I would like to evaluate the content we already have to see if it is still applicable. Then, I'd like to use the relevant information along with some observations I've made through trial and error to achieve the following:

• Craft a complete description of the Coffee Table Groups Lead role
• Identify a comprehensive list of the Coffee Table Groups Lead's duties
• Determine if another Coffee Table Groups volunteer role is needed to support the Coffee Table Groups Lead role
  • Yes, Coffee Table Groups Host role

Resources

Leading a Coffee Table Group page on the website

Collaborators

@abbeyperini and @tkshill – If either of you have any feedback, feel free to contribute!