Code review comment for lp:~ian-clatworthy/bzr/readme-fix

We found a few URLs in README that needed tweaking when putting together the Mac OS X installer. This patch freshens it up for the 2.0 release. I've update the README on pypi (http://pypi.python.org/pypi/bzr/2.0.0) with the proposed new content so reviewers can see what the impact is (on that site at least).