Promenade currently does not define a requirements.txt, meaning that any
pip installations of Promenade do not install any of Promenade's
dependencies. This change adds a link from requirements.txt to the
contents of requirements-direct.txt. This allows requirements.txt to be
defined without immediately altering Promenade's current method of
In the future, Promenade could remove requirements-direct.txt and
requirements-frozen.txt to only utilize a carefully pinned
requirements.txt as many other Airship projects do.