Added a Contributing.md sample

[mmattes]

Open for discussion

[miped]

This is awesome!

[sbuttgereit]

I just read through it. I think it's an excellent start and unless there's objection, I think this should merged.

I do think that new features should likely start out as issues in the issue tracker; probably with a little template that proposes the change, is it an addition or a change to an existing feature etc. With a standard period (maybe a week to start with) to allow community comment. This could be done with a templated PR rather than issues (may be more appropriate)

Having said all that, I don't think too many PRs pulling things in odd directions is a problem right now, so even without setting any of that up, I think this is a good start.

If I don't hear anything to the contrary (and if it hasn't happened yet) I'll go ahead and do the merge on Tuesday evening (my time).

Many thanks for this @mmattes!