docs: restructure README overview and requirements

[joshtrichards]

• Resolves: #

This started with messing around with one paragraph and then it got a bit bigger throughout the day. I think this is an improvement, but I'll let others judge if it's an set of suitable refinements.

Summary

• Rewrite the README introduction and clarify who Nextcloud AIO is intended for
• Reorganize and categorize the Features section, including the expandable list of detailed capabilities
• Add a standalone “How does it work?” (dropping the FAQ entry) section describing (briefly) orchestration, HTTPS, integrations, and customization
• Add a Core Requirements section covering supported platforms, runtimes, domains, architectures, and storage
• Rename the installation walkthrough to “Quickstart”
• Move the architecture overview below the Quickstart section (less overwhelming, more logical needs-driven ordering)
• Improve terminology, formatting, and documentation links throughout the overview

Notes

• The detailed feature list remains collapsed to keep the README easier to scan
• User-count and Enterprise guidance is phrased conservatively. Additionally no secret is made of their being other installation methods.
• Community-maintained containers are explicitly identified as having separate support, update, security, and compatibility considerations.

TODO

• Make sure most of the key hyperlinks are still in place after moving things around / editing

Future follow-up ideas

• Move the FAQ out to a dedicated FAQ.md file.

Summary

• The PR was tested and verified that it works locally
• Or will be tested after merge on a dedicated test instance (available for maintainers)
• Sign-off message is added to all commits
• Tests (playwright if possible) are included
• Screenshots before/after for front-end changes
• Documentation has been updated or is not required
• Labels added where applicable (ex: bug/enhancement, 3. to review, feature component)
• Milestone next added

AI (if applicable)

• The content of this PR was partly or fully generated using AI

[Copilot]

Pull request overview

Restructures the README to improve onboarding and clarify AIO’s audience, capabilities, requirements, and architecture.

Changes:

• Reorganizes features and deployment guidance.
• Adds “How does it work?” and core requirements sections.
• Renames installation instructions to “Quickstart” and moves architecture details.

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