docs: add macOS/Apple Silicon setup FAQ

[lgezz]

Summary

What this adds

A new FAQ documenting how to run OSS-CRS on macOS (Apple Silicon), covering
Docker Desktop + Rosetta setup and the most common Mac-specific errors.

Why

Setting up OSS-CRS on an Apple Silicon Mac surfaces several issues not covered in
the current docs. This FAQ is grounded in a confirmed working end-to-end run of
the crs-libfuzzer pipeline (prepare → build-target → run), producing seeds and
POVs — not speculation.

Contents

• Setup & environment — Docker Desktop vs Colima on Apple Silicon
• The three classic errors, with real root causes:
  • oss-crs-deps: pull access denied — a same-daemon / local-image-not-present
    problem (with docker_registry: local), not a missing registry image;
    includes the post-prepare verification step
  • Killed / exit 137 with empty stderr — ASAN/libFuzzer instability under QEMU
    emulation, resolved by enabling Rosetta
  • Requested CPUs are not available and the cpuset required-field
    constraint — how to set it for a Mac VM
• oss-crs setup — Phase 2 cgroup behavior on macOS and how to proceed
• Running the pipeline — command sequence, the docker-py vs CLI
  DOCKER_HOST gotcha, and how to confirm success via seeds/POVs

Testing / validation

The documented configuration (cpuset: "0-7", memory: "16G", Docker Desktop
with Rosetta, single daemon throughout) was used to complete a full run that
produced seeds and POVs, so the guidance reflects a working setup.

Notes

• Placement per discussion in docs: propose a macOS / Apple Silicon setup FAQ #369
• No functional/code changes; documentation only.
  Signed-off-by: Laura Guazzelli lguazzelli@linuxfoundation.org

[lgezz]

@azchin — would appreciate your review when you have a chance. Thanks!