Add evolving user intent evaluation resource

[natnew]

Summary

Adds LLMs Get Lost in Evolving User Intent to README.md under Evaluation and Testing.

The entry follows the repository's required bullet format, uses the canonical Microsoft Research repository, and describes the concrete AgentOps use case: testing whether agents continue to track user intent when requirements are revealed, revised, or redirected across multi-turn tasks.

Scope

• Updates only README.md.
• Adds the resource to the most specific existing section.
• Uses concise, factual, non-promotional wording.
• Does not alter repository structure or unrelated content.

Resource

• Repository: https://github.com/microsoft/evolving-intent
• Paper: https://arxiv.org/abs/2607.20734