Add DMG creation script

[VihlayewAlex]

Added a script for DMG creation.
Script should be invoked in the DMG directory.
It takes "Alby.app" from "dmg_content" directory and creates a DMG file

Resolves #1

[bumi]

Great! can you add some explanation to the readme what needs to be done to run it.
e.g. create the Alby.app, put it in the dmg_content folder, run the script, etc.

[stuffmc]

Bad Idea. The dmg thing had always been this weird series of anachronistic steps. Like, okay, now mount a disk image (do what?) now don’t open the app. (Well you could but don’t) instead, drag the app to this folder that is a shortcut (a what?) that leads to your Applications folder. (My what?) okay, now eject the dmg (sorry, what?) and the go to your applications folder. (Is that my dock? Or maybe my launch pad?) now find it in your Applications folder and open it there.