docs: Update marketing README.md & Add sponsorship.md

[syedjawadakhtar]

Checklist

• [x] Updates #31
• [x] Passes Semantic Pull Request and TypoCheck
• [x] New docs are listed in README.md
• [ ] New docs are listed in index.md
• [ ] Updated table of content
• [ ] Updated nav links in mkdocs.yml

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PR description

1. Add link to sponsorship.md in README.md
2. Add file sponsorship.md

[pnijhara]

Please update these links in the nav bar.