create a new section of the getting started page that lets people know

create a new section of the getting started page that lets people know
that they should install monkeysphere software at this point in their
journey. It may be obvious, but I think in terms of providing a
step-by-step howto get started guide, the least assumptions of
obviousness we make, the better.

I also moved the information about making sure that you have the
gnutls requirements up to this install section.