Update install information

- using brew on mac OXS
- avoid redundant info between README and MANUAL
On Mon, Aug 25, 2014 at 07:59:47AM -0700, Mehdi Amini wrote:
> In omp/__init__.py:
> >
> >
> >  class omp(object):
> >      paths = (
> >          # find_library() does not search automatically LD_LIBRARY_PATH
> >          os.environ.get('LD_LIBRARY_PATH', '').split(':')
> > -        + [  # Default gcc path on debian/ubuntu (?)
> > -            &quot;/usr/lib/x86_64-linux-gnu/&quot;,
> > -        ]
> > -        # MacPorts install gcc in a &quot;non standard&quot; path on OSX
> > -        + glob.glob(&quot;/opt/local/lib/gcc*/&quot;)
> > -    )
> > +        + [check_output([cxx, '-print-file-name=libgomp.so']).strip()])
> $ g++-mp-4.8 -print-file-name=libgomp.so
> libgomp.so

And what about s/libgomp/libgcc/?