New instructions for new contributors to the Narayana project

[Michael Musgrove]

They are not so new, rather a formalisation of much of what we already require from new contributors. I raised a PR (https://github.com/jbosstm/narayana/pull/1746/files) to update the instructions. I took, as a starting point, the CONTRIBUTING.md text that the quarkus project asks for and tweaked that for our particular needs. The reviewers of my PR have asked me to take the proposal to a broader audience, which is anyone reading this post :) 

If you have any feedback or disagree with the approach please could you let us know, either here or on the PR.

Thanks