Build .dmg automatically for MacOS

[Adam Winer]

Original [issue 19](https://code.google.com/p/scythebill-birdlist/issues/detail?id=19) created by adam_winer on 2010-11-05T23:37:03.000Z:

See: http://stackoverflow.com/questions/96882/how-do-i-create-a-nice-looking-dmg-for-mac-os-x-using-command-line-tools

... for some suggestions