* Revised and expanded contribution guidelines
* Added some extra links and reordered
* Reworded substantially following Dave Hudson's feedback. Incorporated James's feedback too
* fixed urls
* capital letter after colons if they are the start of a new sentence
* Named Joel as a maintainer
* Linked to docsite mechanics page
* simplified some of the wording
* Said R3 Alliance the first time R3 is mentioned and clarified that R3 implies R3 Alliance
* merged the two "how to contribute" sections