Adding first draft of contributing guidelines

[jc00ke]

Github just pushed the contributing guidelines feature:
https://github.com/blog/1184-contributing-guidelines

@brixen @dbussink @evanphx thoughts?

[dbussink]

Ok, few initial thoughts:

• Add a request for a reproduction of the issue. It is usually not very useful if people report a crash / bug without telling us how they got it. This often results in going back and forth in the issue before we have something actionable. Basically the smaller / easier the repro, the faster it is fixed usually. Issues without a way to reproduce them often linger around for a long time.
• If you add a spec and a bugfix, it's not necessary to also add tags. We don't have an explicit guarantee that every commit should be green, but just that every push / merge should be. We don't want to add that overhead to contributors if it's not necessary.
• Maybe add a comment on style for larger commit messages? So have a single line title message up to (I think) 80 characters (my vim setup actually shows when I go over it, so don't know the actual limit) and use separate paragraphs afterwards for more detail.

[leavengood]

To respond to the last bullet point from dbussink, generally the first line in Git should not be more than 50 characters. Here is some general advice on Git commit messages:

http://tbaggery.com/2008/04/19/a-note-about-git-commit-messages.html

[jc00ke]

I prefer @tpope's method.

[ghost]

Could we break this line up into multiple lines? (e.g: a paragraph split by newlines).
On smaller screens this forces horizontal scrolling, which sucks :P

[carlosgaldino]

Since this branch was public I took the liberty of splitting the long lines.

@jc00ke
I hope you don't mind. =)

[jc00ke]

Nope, I don't mind at all! When I was typing that line out it felt long, but I wasn't sure if it would wrap or scroll on GH.

I think this is a good start. I'll merge now, and we can change if needed.