docs: add reference to local resolver provider

[nicklasl]

Summary

• Adds a callout near the top of the README pointing users to the Confidence Local Resolver Provider for Java for better resilience and lower latency.
• Adds a [!TIP] note before the OpenFeature quickstart code section with the same recommendation.

Test plan

• Verify README renders correctly on GitHub

🤖 Generated with Claude Code

[vahidlazio]

LGTM