[Feature]: LLM.txt file for AI-Assisted Coding

### What would you like?

I would like for an LLM.txt file to be provided by the durable functions sdk so that I can use AI Coding agents to help me build my durable function workflows.

### Possible Implementation

_No response_

### Is this a breaking change?

No

### Does this require an RFC?

No

### Additional Context

_No response_