Update install information

- using brew on mac OXS
- avoid redundant info between README and MANUAL
On Mon, Aug 25, 2014 at 08:03:13AM -0700, Mehdi Amini wrote:
> In pythran/pythran-darwin.cfg:
> > @@ -0,0 +1,14 @@
> > +[sys]
> > +
> > +cppflags = -DENABLE_PYTHON_MODULE -DUSE_GMP -
> DBOOST_SIMD_CONFIG_SUPPORT_POSIX_MEMALIGN
> > +cxxflags = -std=c++11
> > +ldflags =   -lboost_python-mt
> > +            -lgmp
> > +            -lgmpxx
> > +
> > +[user]
> > +
> > +cxx = g++
> why?

A bug in boost simd that prevents the detection of this intrisic on some
friend's Mac OSX. This should be removed once the nt2 version is
patched.