Update README.rst with required Mac Homebrew step
Update README.rst with required Mac Homebrew step

After googling to https://github.com/kennethreitz/autoenv/issues/41 and https://github.com/kennethreitz/autoenv/pull/51 I finally did this to make autoenv work.
waxzce/autoenv,cehoffman/autoenv,cehoffman/autoenv,waxzce/autoenv,kennethreitz/autoenv,kennethreitz/autoenv