Code review comment for lp:~hazmat/pyjuju/formula-upgrades-spec

Thanks for the review ben, 1-2 addressed. Re 3, there are lots of additional contextually relevant items for upgrades which will need deeper delving in the future.

> Looks good overall, thanks.
>
> [1]
> + The ``upgrade-formula`` hook will likely need access to a new cli-api
> +to access all relations of the unit, in addition to the standard hook
> +api commands like ``relation-list``, ``relation-get``,
> +``relation-list``.
>
> relation-list appears twice
>
>
> [2]
>
> Maybe link to the forumla spec in reference to defining version.
>
>
> [3]
>
> There are still lots of open areas pointed at by the docs that ate my other
> questions by defining them as out of scope.