Adding CONTRIBUTING document

Following up on the Hydra Tech Call agenda item 2014-10-08.3.e, this
is an initial straw person to push against and help form the ongoing
process for collaborating on Hydra::Works

See the following link for reference:

  https://wiki.duraspace.org/display/hydra/Hydra+Tech+Call+2014-10-08

Related to projecthydra-labs/hydra-works#6