Add Gempix2 link to README

[tkaptop]

描述：

Summary

Proposing to add Gempix2 (Nano Banana 2) - a free AI image generation service.

Description

• Model: Gempix2 (Nano Banana 2) - second-generation image generation model
• Primary Functions: Text-to-image generation and AI-based image editing
• Additional Features: Video generation support (VEO3.1, Sora 2)
• Access: Free, no registration required
• Status: Production, actively maintained

Why Include It

Gempix2 (Nano Banana 2) provides free access to a production-grade image generation model, addressing the common barrier of cost in AI tools.

Thank you for considering this addition.