Update README.md

Homebrew recently booted a bunch of Formulae to their science repository, VIPS has been included in the move. 

I opened up a ticket about this with Homebrew as the change has frustrated me a great deal and I think makes it substantially less easy to use.

Regardless, for the mean time, this is how to install VIPS via homebrew now.
Merge pull request #33 from tehprofessor/patch-1

Update README.md
README updates

Update README OS X notes for the latest homebrew.
test polishing for vips-7.34
more spec fixes

don't test a sha1 hash for results from external libraries
first try and sort-of works

try:

----------

require 'rubygems'
require 'vips'

include VIPS

data = IO.read('/home/john/pics/shark.jpg')

reader = JPEGReader.new(data, :shrink_factor => 2, :fail_on_warn =>
true)

im = reader.read_buffer

im.write('out.png')
----------
cleanups for new buffer read

use vips8 API for buffer read/write stuff, if possible, it improves
compatibility

fix an oops in version #if-ing
Ooops argh

another compat oops fixup
README oops
add png memory load

needs vips-7.34 or later

also improved vips lib version testing
add spec tests for buffer load

the new png and jpg load from buffer paths now have spec tests
more robust png save tests
add C sources to rdoc build
fix up some more tests

and a VIPS:: was missing, oops
better version test on jpeg read/write
better compat with older libvips

also, turn on rdoc2+ test version filtering
don't test against ruby-head

it's failing for some strange config reason
Regenerate gemspec for version 0.3.6
Merge branch 'master' of git://github.com/jcupitt/ruby-vips