Update objectives.rst to be explicit about which Filesystem API we will use (and some other things?)

<zancas> The only one that was substantive was to the "Normaliation and
         Sustainability" section.  I had difficulty following the startup
         culture-practices--list of risks flow.
<zancas> Thought on objectives:  [15:04]
<zancas> Perhaps for objective 1 we should assert that we're _probably_ going
         to use _one_ of the filesystem-change-detection APIs, and simply
         mention that we're aware of the other.  [15:05]
<zancas> As it reads now, it seems (correctly?) that we know very little about
         either API, and either might be selected.
<zancas> My hunch is that we know more about their tradeoffs, if that hunch is
         correct, then we should make it seem like we have the know-how that
         we do.  [15:06]
<zancas> e.g.  I bet we could ask Darius, Daira, or someone who could tell us
         which is a better choice and why.
<zancas> Then we could change objective 1 to say we're familiar with API X,
         and will likely use it, but for completeness we'll consider API Y as
         well.  [15:07]