fetch contributor names from $zilla->distmeta->{x_contributors}
insert stopwords into document directly with "=for stopwords ..."

This lets us avoid having to mess around with the %PodWeaver stash -- as the
plugin will still see the words this way -- and also allows other tools, such
as Pod::Spell, to see the stopwords without requiring the [StopWords] plugin
have to do it for us.