Our CLI docs are very out of date. These used to be generated by the
docs team with some tooling they had. Since the docs moved in-repo, that
tooling has gone away, and for the most part no one has done any updates
to the CLI docs.

This adds a sphinx directive that will generate these docs every time
the docs are built. This way, whenever someone makes a CLI change, they
do not need to have to know to also edit a documentation file to match
their change. Any code changes will automatically be picked up and
reflected in the docs.

Change-Id: I4406872ab6e9335e338b710e492171580df74fa5
Signed-off-by: Sean McGinnis <sean.mcginnis@gmail.com>