Enhance the contributing guide documentation

Currently, the [contributing doc](https://github.com/cloud-ark/kubeplus/blob/master/Contributing.md) only covers the submission of feature requests and bug reports. We should also include how to submit patches. This will require setting up [a development environment](http://kubeplus-docs.s3-website-us-west-2.amazonaws.com/html/compile-components.html). 
