docs: restructure Getting Started with prerequisites and clearer sect…

[anishasingh-dev]

…ions

This change improves the Getting Started documentation by restructuring the content and adding a clear Prerequisites section.

The guide is now easier to follow for new contributors, with better sectioning, clearer setup steps, and improved readability without changing any technical behavior.

Make sure these boxes are checked before your pull request (PR) is ready to be reviewed and merged. Thanks!

• tests pass -- look for a green checkbox ✔️ a few minutes after opening your PR -- or run tests locally with rake test
• code is in uniquely-named feature branch and has no merge conflicts
• PR is descriptively titled
• PR body includes fixes #0000-style reference to original issue #
• ask @publiclab/reviewers for help, in a comment below

We're happy to help you get this ready -- don't be afraid to ask for help, and don't be discouraged if your tests fail at first!

If tests do fail, click on the red X to learn why by reading the logs.

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We have a loose schedule of reviewing and pulling in changes every Tuesday and Friday, and publishing changes on Fridays.

Thanks!

[anishasingh-dev]

Thanks! This PR only updates documentation and does not change any code.
Happy to make adjustments if needed.