[Feature]: Add support for `instructions` according to MCP standart

[everm1nd]

Problem statement

https://modelcontextprotocol.io/specification/draft/schema#initializeresult-instructions

Instructions describing how to use the server and its features.

Instructions should focus on information that helps the model use the server effectively (e.g., cross-tool
relationships, workflow patterns, constraints), but should not duplicate information already in tool descriptions.

Proposed solution

Add instructions field to xmcp.config

Package

xmcp (core framework)

[everm1nd]

@0xKoller supersonic 🔥 🙏

[0xKoller]

@0xKoller supersonic 🔥 🙏

Thanks for the using xmcp and opening issues!

[wessmeister]

+1, this would be really cool to have!