Guide: explains the enum/match relationship

Closes #18169
@gamazeps I'm not a native speaker either, so maybe someone else wants to way in. I was actually close to suggesting "(Movie)Extra", or "Bystander" as an alternative, but my gut feeling is that it would just be better to avoid "Who cares about $person's name" altogether. (The Peon wording in particular invokes "We are the mighty rulers, we don't care about those simple people" imagery in my head)