Add 'Getting Started' message to README.rst

Quoting gsilvis (2014-06-24 10:03:09)
> > +This assumes that you are using the bash shell.  For other shells, see the
> > +other files in the directory ``.venv/bin``. Then, once you are ready to test
> > +the *haas* code, run::
> > +
> > +  pip install -e .
> > +
> > +Now ``haas`` will be in your path, and you can run it.  However, if you are
> > +running a Debian Wheezy system (among possibly others), you will get the
> > +following error::
> 
>    Actually, I don't like that either. How about: "On systems with an
>    older version of pip, such as Debian Wheezy and Ubuntu 12.04, this will
>    fail with:: [message]. To fix this, upgrade pip within the virtual
>    environment. (You only need to do this once.) [pip upgrade command].

That's better, but I might even put the upgrade bit before the `pip
install -e .` command.