docs: use main branch for README logo assets

[pavan-sh]

Summary

The README logo assets across the repo are currently hotlinked from the moving HEAD ref on GitHub raw URLs.
This PR updates those logo URLs to point to the stable main branch instead.

Test plan

• Ran Prettier check on the modified README files:
• pnpm prettier --check README.md packages/@tailwindcss-*/README.md packages/tailwindcss/README.md
• Verified the README logo URLs now use .../tailwindcss/main/.github/logo-*.svg.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

---

Walkthrough

This pull request updates image source URLs across multiple README files from HEAD branch references to main branch references. Specifically, dark and light logo srcset paths and img src attributes in centered logo blocks are changed from HEAD/.github/logo-*.svg to main/.github/logo-*.svg in the root README and eight package-specific README files. Each file receives the same three-line modification to its logo asset references, with no changes to documentation structure or content beyond the branch reference updates.

🚥 Pre-merge checks | ✅ 2

✅ Passed checks (2 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and concisely summarizes the main change: updating README logo assets to use the main branch instead of HEAD.
Description check	✅ Passed	The description is directly related to the changeset, explaining the motivation (replacing moving HEAD refs with stable main branch) and providing test verification details.

_{✏️ Tip: You can configure your own custom pre-merge checks in the settings.}

---

Thanks for using CodeRabbit! It's free for OSS, and your support helps us grow. If you like it, consider giving us a shout-out.

❤️ Share

• X
• Mastodon
• Reddit
• LinkedIn

_{Comment @coderabbitai help to get the list of available commands and usage tips.}

[RobinMalfait]

Hey! Thanks for the PR, but HEAD is fine in this case.

[pavan-sh]

Hey! Thanks for the PR, but HEAD is fine in this case.

Cool, thanks for the review and valuable time.