README: document getting started process

The old instructions were rather dense and I believe out of date.
Replace it with this set of instructions.

Move the local-setup script to contrib/osx in anticipation for a
contrib/linux and contrib/k8s setup.

contrib/osx/local-setup.sh

@@ -0,0 +1,23 @@
+#!/bin/bash
+
+# Put us at the root of the quay repo no matter what
+pushd $(dirname "${0}") > /dev/null
+basedir=$(pwd -L)
+cd "${basedir}"/../../
+
+# Install Docker and C libraries on which Python libraries are dependent
+brew update
+brew upgrade
+brew install boot2docker docker libevent libmagic postgresql gpgme
+
+# Some OSX installs don't have /usr/include, which is required for finding SASL headers for our LDAP library
+if [ ! -e /usr/include ]; then
+    sudo ln -s `xcrun --show-sdk-path`/usr/include /usr/include
+fi
+
+# Install Python dependencies
+sudo pip install -r requirements.txt
+
+# Put the local testing config in place
+git clone git@github.com:coreos-inc/quay-config.git ../quay-config
+ln -s ../../quay-config/local conf/stack