Clarify NewSlide positioning and add community/sponsorship scaffolding

[Copilot]

NewSlide’s differentiator is slide-change-driven segmentation rather than silence/time chunking, and the repo needed contributor/sponsorship scaffolding to support growth. This PR adds that positioning to docs and wires the basic project-community files.

• README: product positioning

  • Added a focused “Why NewSlide” section that highlights slide-aware segmentation as the core distinction.
  • Kept the core mechanism and prototype usage flow intact while making the value proposition faster to scan.

• Contributor onboarding

  • Added CONTRIBUTING.md with:
    • contribution entry points (good first issue, help wanted)
    • local setup prerequisites
    • coding/style expectations
    • PR checklist and label taxonomy

• Sponsorship wiring

  • Added .github/FUNDING.yml so the repo can expose sponsor/funding links.

# .github/FUNDING.yml
github: [ATECCA]
custom: ["https://opencollective.com/"]