Proposal: Modernizing Generative AI README and fixing grammatical inconsistencies

[HassanFleyah]

Description

I would like to propose an update to the generative_ai/README.md file. The current documentation contains some grammatical inconsistencies in the "Getting Started" section and refers to older model versions (Gemini 1.5).

Proposed Changes

1. Grammar Fix: Correct the sentence structure in the "Getting Started" section to improve readability.
2. Modernization: Update the feature table to reflect 2026 standards and ensure model references are current.
3. Security: Add a brief note about credential management best practices (ADC/Secret Manager) for users running samples locally.

I have already prepared the changes in a fork and I'm ready to submit a Pull Request if this proposal is accepted.