docs: propose a macOS / Apple Silicon setup FAQ

Summary

I recently set up and ran OSS-CRS (crs-libfuzzer) end-to-end on an Apple Silicon
Mac and hit several macOS-specific issues that weren't covered in the existing
docs. After working through them to a successful run (full prepare → build-target
→ run pipeline, producing seeds and POVs), I wrote up an FAQ and would like to
contribute it as documentation.

What the FAQ covers

• Docker Desktop + Rosetta setup for reliably running the amd64 fuzzing images on
  Apple Silicon
• The three most common errors on Mac and their actual root causes:
  • oss-crs-deps: pull access denied — really a "prepare and build-target hit
    different daemons / local image not present" problem, not a registry issue
  • Fuzzer dies with Killed (exit 137) — ASAN/libFuzzer instability under QEMU
    emulation; resolved by enabling Rosetta
  • cpuset handling — it's a required schema field (can't be deleted), and how
    to set it for a Mac VM
• oss-crs setup Phase 2 behavior on macOS (the /etc/docker/daemon.json
  cgroup step doesn't apply cleanly) and how to proceed
• How to confirm a successful run (seeds / POVs under SUBMIT_DIR)

Questions before I open a PR

1. Would you welcome this as documentation? It's grounded in a confirmed working
   configuration, not speculation.
2. Where would you prefer it live — e.g. docs/faq-macos.md, a section in an
   existing doc, or somewhere else?
3. Should I also link it from the README, or do you have a docs index it should
   go into?

Happy to open the PR as soon as you confirm placement. Thanks!

Review the existing documentation and README to determine the preferred location and linking convention; the proposed path is docs/faq-macos.md. Use the confirmed Docker Desktop, Rosetta, cpuset, setup, and successful-run details from the issue. Done when the FAQ explains the listed macOS problems and how to verify seeds and POVs under SUBMIT_DIR.