Clarify purpose of local/upstream extras
Clarify purpose of local/upstream extras

jaraco/jaraco.context,jazzband/inflect,jaraco/irc,jaraco/rwt,yougov/pmxbot,jaraco/jaraco.classes,jaraco/jaraco.path,jaraco/jaraco.text,jaraco/keyring,jaraco/jaraco.functools,jaraco/hgtools,jaraco/jaraco.logging,jaraco/calendra,jaraco/backports.functools_lru_cache,yougov/pmxbot,jaraco/tempora,jaraco/portend,pytest-dev/pytest-runner,yougov/pmxbot,jaraco/jaraco.itertools,python/importlib_metadata,jaraco/jaraco.stream,pwdyson/inflect.py,hugovk/inflect.py,jaraco/zipp,jaraco/jaraco.collections