Site doesn't auto-doc rule triggers

[dgw]

Previous discussion: sopel-irc/sopel#311

This could be tricky, but probably less so with recent enhancements in Sopel.

I still expect it to be a bit hack-y, and we definitely need to make an exception for .*, but whatever we come up with for this can be translated to the plugins database site later if that grows to include a list of triggers for each plugin. It'd be great to have at least a tool to generate those on-demand, if not keep it up-to-date automatically (tech stack for that project is still not final).