docs: add sponsor section to README with UTM-tagged Modem link (GTM-29)

[TaltonFiggins]

Summary

Adds a ## Sponsor section to the README pointing back to modem.dev with the canonical UTM tagging from the GTM UTM Tagging Strategy. Mirrors the same pattern already shipped in modem-dev/slop-scan.

The prior ## About blurb ("Brought to you by the team at Modem…") was removed — its taglining role overlapped with the sponsor section, and the slop-scan template doesn't carry one.

Linear

GTM-29 — Add "Sponsored by Modem" section to baudbot README with UTM-tagged link

Changes

• Add ## Sponsor section above ## License with text link + dark/light Modem logo
• Sponsor link: https://modem.dev?utm_source=github&utm_medium=oss&utm_campaign=oss_baudbot&utm_content=readme_footer
• Remove the prior ## About section (replaced by the sponsor block)

Testing

• Section renders correctly in GitHub markdown preview
• After merge: confirm a $pageview lands in PostHog with utm_campaign=oss_baudbot within ~24h of the first click

Related

• UTM Generator row registered for this link (Notion)
• Slop-scan, hunk, podguy still use the older utm_campaign=<repo> form — separately tracked in GTM-32 for migration

[greptile-apps]

Greptile Summary

Replaces the old ## About blurb with a structured ## Sponsor section containing a UTM-tagged text link and a dark/light adaptive logo image, then moves ## License to the bottom.

• The <picture>/<source media=\"(prefers-color-scheme: …)\"> pattern correctly adapts the logo for GitHub's dark and light themes, with the black logo as the fallback <img> for browsers that don't support <picture>.
• Both the text link and the logo anchor carry identical UTM parameters (utm_content=readme_footer), meaning click-through analytics will not distinguish text clicks from logo clicks — this appears intentional given the single readme_footer content slot defined in the GTM UTM strategy.

Confidence Score: 5/5

Documentation-only change with no functional code; safe to merge.

The change touches only README.md, adding a sponsor block with a UTM-tagged link and an adaptive logo. The UTM parameters in the diff exactly match those documented in the PR description, the picture dark/light pattern is correct, and the removed About section is cleanly replaced. No logic, dependencies, or configuration are affected.

No files require special attention.

Important Files Changed

Filename	Overview
README.md	Adds a ## Sponsor section with a UTM-tagged text link and dark/light logo using a <picture> element; removes the old ## About blurb; moves ## License to the end.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A["README.md (before)"] --> B["## About\n(Brought to you by Modem…)"]
    A --> C["## License\nMIT"]
    D["README.md (after)"] --> E["## Sponsor\nText link + picture element\n(UTM-tagged)"]
    D --> F["## License\nMIT"]
    B -.->|"removed"| E
    C -.->|"moved below Sponsor"| F

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