chore(803): improve contribution guidance for developers

[JohnTParsons]

closes #803

What

1. Background - we are welcoming external contributors to newskit
2. What did you do - add CONTRIBUTING.md and edit README.md
3. What does the reviewers should expect - preview the markdown changes by going to
   https://github.com/newscorp-ghfb/NewsKit/blob/chore/803-contribution-guidance/CONTRIBUTING.md
   and
   https://github.com/newscorp-ghfb/NewsKit/tree/chore/803-contribution-guidance#readme (the new link to it in README.md)

I have done:

• Written unit tests against changes
• Written functional tests against the component and/or NewsKit site
• Updated relevant documentation

I have tested manually:

• The feature's functionality is working as expected on Chrome, Firefox, Safari and Edge
• The screen reader reads and flows through the elements as expected.
• There are no new errors in the browser console coming from this PR.
• When visual test is not added, it renders correctly on different browsers and mobile viewports (Safari, Firefox, small mobile viewport, tablet)
• The Playground feature is working as expected

Before:

After:

Who should review this PR:

How to test:

[pp-serviceaccount]

You can preview these changes on:
Documentation Site: http://ncu-newskit-docs-pr.s3-website-eu-west-1.amazonaws.com/803-contribution-guidance
Storybook: http://ncu-newskit-docs-pr.s3-website-eu-west-1.amazonaws.com/803-contribution-guidance/storybook

[Vanals]

As above!

Also I think they can open issues even if is not clear to them what the problem is, as far as is a bug for instance it is fine for them to open an Issue IMO. So Again I would explain the two path Question and Bug/Feature separately. from a question. Feels a bit mixed now

[JohnTParsons]

Have now combined the information from the original Ask a Question and Suggesting Enhancements sections to reduce the repetition

[jps]

looking good! 💯