Make "CONTRIBUTING" general testing steps clearer, easier to edit and expand upon.

[freephile]

I think if we convert 'CONTRIBUTING.md' to wiki page or series of wiki pages, they will become more useful than a markdown file within the project source.

[freephile]

Once upon a time, all the documentation lived in the project as markdown. Now, almost all of it except the README and CONTRIBUTING files have been converted to wiki pages. While it's easier for a developer to edit the markdown files in the project src tree, there's an advantage to the wiki approach to documentation because any user can update and add or organize documentation. What's more, the wiki approach adds much greater flexibility to add diagrams and even videos with ease.