docs: add quick start, dev setup & troubleshooting (Fixes #1407)

[kkrishnan10]

Fixes #1407
This pull request updates the documentation to make it easier for new users and first-time contributors.
I added:

• a Quick Start section with install and first-run steps
• a short Dev Setup (TL;DR) for building locally
• a Troubleshooting section for common setup issues
• and a First Contribution Checklist to guide new contributors
  These updates are documentation-only (README.md and docs/build-and-run.md).
  No code changes or build impact.
  I checked that the Markdown formatting looks good and that all the links work correctly in GitHub’s preview. Since this is just a docs update, no functional testing was needed.

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