document how to create alternate Cask Taps

[rolandwalker]

closes #3954

[kevinoconnor7]

In regards to rejecting apps, especially with #3954, there should probably be documentation outlining some restrictions that might lead to maintainers rejecting an app. To counteract the hit to the goal of being an open platform, you might also want to require the majority of maintainers to agree to reject a cask.

Formalizing the process should make future situations like #3954 go smoother. Especially since pretty much all of the maintainers have been in agreement since my initial PR (#3582).

Sorry that this is a bit off-topic for this PR, just wanted to bring it up since it is mentioned in these documentation amendments.

[tapeinosyne]

There was a tedious, fruitless discussion on IRC about admissibility guidelines and rejection policy where no consensus emerged; I suspect most of the core maintainers are not very eager to repeat the experience.

My suggestion would be to merge the docs and forget about the matter: a painless way to create unofficial repos might be sufficient to swiftly extinguish debates around admissibility.

[rolandwalker]

@kevinoconnor7 I agree that general policies might be a nice thing, but since there is not a consensus among the maintainers, I cannot fairly document them. In the meantime, the GitHub Terms of Service serve as a reasonable guide.