Update README.md

[thomasbuilds]

• Replaced the root README.md with a symlink to packages/solid/README.md to eliminate duplication and centralize documentation.
• Standardized README badges to match the style used across the broader Solid ecosystem.
• Updated onboarding instructions to reflect the current recommended workflow using npm create solid.
• Improved overall structure and wording for better readability and quicker comprehension.
• Refined key sections, including core features, quick start, ecosystem links, and contribution/support (replacing hardcoded <a> links with dynamic Open Collective SVGs).
• Added references to the wider Solid ecosystem (e.g., SolidStart, Solid Router, etc.).
• Removed the unused and outdated banner.png.

[changeset-bot]

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Latest commit: 072b881

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