Brainstorm a first table of contents for a new merchants section

[GBKS]

As discussed in jam session #24, there is interest in creating a merchant section. To get this effort off the ground, a good exercise would be to brainstorm what content to include. This will also help us decide what not to include, what to prioritize, etc. This is similar to what we did at the beginning of the guide project.

Join the discussion in the #merchants channel on Slack. We have a Google Doc floating around to gather ideas.