Adding CONTRIBUTING.mdown
Adding CONTRIBUTING.mdown

Inspired by Ceeram's PR in

	https://github.com/cakephp/cakephp/pull/1173/

rakeshtembhurne/croogo,Wouter0100/croogo,cvo-technologies/croogo,xintesa/croogo,cvo-technologies/croogo,rakeshtembhurne/croogo,rchavik/croogo,xintesa/croogo,rchavik/croogo,delkyd/croogo,xintesa/croogo,delkyd/croogo,Wouter0100/croogo,rakeshtembhurne/croogo,delkyd/croogo,cvo-technologies/croogo,damien-biasotto/croogo,Wouter0100/croogo,damien-biasotto/croogo