docs: restructure run tests documentation

[MikeMcC399]

Goals

In the README the goals are:

• simplification for first-time users
• more clarity in the documentation between local / CI testing, usage and support
• preparation to add information about running Docker, so that the structures will be able to fit. (The plan is to mark the CI examples which use Docker and add explicit instructions about running the repo in Docker locally.)

Change

This PR restructures the README section about running tests.

It starts from a set of instructions to clone and run, which can be simply copied and pasted. It explains then in more detail about options and what happens behind the scenes.

Local testing and CI testing are clearly separated.

Documentation and getting help are also separated from the instructions about running tests.

The link to the 5 year old CHANGELOG_OLD.md in the README is also removed as this is now very old and no longer needed / helpful. The file itself is left in place

[cypress-app-bot]

• Create a Draft Pull Request if your PR is not ready for review. Mark the PR as Ready for Review when you're ready for a Cypress team member to review the PR.

[cypress-app-bot]

🎉 This PR is included in version 3.1.1 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

Your semantic-release bot 📦🚀