Added CONTRIBUTING.md

Signed-off-by: Patrick Cozzi <pjcozzi@gmail.com>
CONTRIBUTING.md wording tweaks

Signed-off-by: Patrick Cozzi <pjcozzi@gmail.com>
More CONTRIBUTING.md tweaks

Signed-off-by: Patrick Cozzi <pjcozzi@gmail.com>
Attempt to workaround markdown formatting

Signed-off-by: Patrick Cozzi <pjcozzi@gmail.com>
Fixed typo

Signed-off-by: Patrick Cozzi <pjcozzi@gmail.com>
Merge pull request #540 from AnalyticalGraphicsInc/contribute

Added DCO and CONTRIBUTING.md