readme: Remove some old info [ci skip]

Signed-off-by: BJ Hargrave <bj@bjhargrave.com>
contributing: Define contribution rules and triangular workflow [ci skip]

We plan to move to a triangular workflow and developer certificate of
origin for bnd. This document describes the workflow and how to set it
up.

Credit to docker for the contributing document.
https://github.com/dotcloud/docker/blob/master/CONTRIBUTING.md

Signed-off-by: BJ Hargrave <bj@bjhargrave.com>
Merge pull request #535 from bjhargrave/master

Document proposed new triangular workflow and developer certificate of origin