Enhance README: Shields to capture the attention of potential contributors

[devactivity-team]

I noticed you have opened issues labeled help wanted. I recommend enhancing the README to make the call for new contributors more prominent.

Changes Made:

1. Shields: Added Shields.io badges at the top of the README

[![GitHub repo Good Issues for newbies](https://img.shields.io/github/issues/valtiojs/valtio-yjs/good%20first%20issue?style=flat&logo=github&logoColor=green&label=Good%20First%20issues)](https://github.com/valtiojs/valtio-yjs/issues?q=is%3Aopen+is%3Aissue+label%3A%22good+first+issue%22) [![GitHub Help Wanted issues](https://img.shields.io/github/issues/valtiojs/valtio-yjs/help%20wanted?style=flat&logo=github&logoColor=b545d1&label=%22Help%20Wanted%22%20issues)](https://github.com/valtiojs/valtio-yjs/issues?q=is%3Aopen+is%3Aissue+label%3A%22help+wanted%22) [![GitHub Help Wanted PRs](https://img.shields.io/github/issues-pr/valtiojs/valtio-yjs/help%20wanted?style=flat&logo=github&logoColor=b545d1&label=%22Help%20Wanted%22%20PRs)](https://github.com/valtiojs/valtio-yjs/pulls?q=is%3Aopen+is%3Aissue+label%3A%22help+wanted%22) [![GitHub repo Issues](https://img.shields.io/github/issues/valtiojs/valtio-yjs?style=flat&logo=github&logoColor=red&label=Issues)](https://github.com/valtiojs/valtio-yjs/issues?q=is%3Aopen)

2. Welcoming Message: Enhanced the README with a more prominent and inviting message to welcome new contributors.

Why This Matters:

• Attract New Contributors: Considering there is a number of opened issues labeled 'Help Wanted' - a welcoming and appealing README is one of the most efficient ways to attract new contributors

Additional Resources:

For more insights into building a strong open-source community, check out the Building Community guide.

🚀 Thank you for considering this pull request! 🚀

[devactivity-team]

I also suggest enhancing the README with the following widgets using devActivity app:

1. Dynamic Top Contributors (with avatars linked to contributor profiles)

2. Repo Stats

Feel free to explore the Live Demo and Public Dashboard for a quick overview of the app.
It makes the contribution process more exciting with gamification elements like:

• 🌟 XP and Levels based on contributions
• 🏆 Challenges and Achievements
• 🏅 Leaderboard and much more!

Latest repositories using devActivity: barecheck (⭐55)

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Simply install an app to bring a more comprehensive and engaging community experience.

🌟 Happy Coding! 🌟

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[dai-shi]

I like using img.shelds.io as we already use it, but in general, I don't think it's super important or necessary for getting helps.

Thanks for your suggestion. Let's see for a while if we get more comments on it from others before closing.