[Doc] add langchain/langgraph integration guide

[furykerry]

document how to integrate langchain/langgraph with openkruise agents using E2B api

[kajal-jotwani]

/assign

[Daiwik-1901]

/assign

[Daiwik-1901]

I wanted to ask where you’d prefer this guide to live in the repo — for example under docs/, an integrations/ subdirectory, or another location you recommend.