Document trilogy's variation on the packaged_source strategy

Trilogy concatenates all the packaged source into a single C file, see https://github.com/github/trilogy/blob/main/contrib/ruby/ext/trilogy-ruby/extconf.rb#L5

which is a notable variation from what we do with libyaml in https://github.com/flavorjones/ruby-c-extensions-explained/tree/main/packaged_source