Add reference to FDE Interview Handbook for Forward Deployed Engineer roles

Summary

FDE (Forward Deployed Engineer) interviews cover a unique set of topics not addressed in most SWE guides — agentic system design, live demo rounds, customer-facing case studies, and LLM deployment questions. This is a growing role category at companies like Palantir, Databricks, Scale AI, Anduril, and Google.

I'd like to add a short section to the README pointing readers toward the FDE Interview Handbook — a free, curated resource specifically for FDE interview prep.

This is especially useful for software engineers pivoting into Forward Deployed Engineer roles — where your code ships inside customer environments, not just your own infrastructure.

Proposed addition: A brief "Looking for Forward Deployed Engineer (FDE) content?" section, similar to the existing "Looking for Front End content?" section.

Happy to submit a PR if this is welcome!