Readme updates

[EiffL]

This pull request updates the README.md to reflect the latest status of the AION-1 model, improves clarity, and adds new acknowledgments. The most important changes include removing outdated alpha testing instructions, updating model variant information, and adding new badges and acknowledgments.

Documentation and usability improvements:

• Removed the "Alpha Testing" section and related Hugging Face access instructions, since the model is now publicly available.
• Updated the model variants table to include direct links to the available model and indicate future releases.
• Added new badges for arXiv and Hugging Face model availability, and updated navigation links to include tutorials.
• Removed reference to online documentation for clarity in the quick start section.

Acknowledgments:

• Expanded the acknowledgments section to credit supporting organizations and computing resources.