v2.0.1: ship macOS download-fix helper + docs
Bump project version to 2.0.1. Add scripts/macos-fix-download.sh
(dequarantine + ad-hoc re-sign + verify) and install it at the archive
root on macOS. Replace docs/macOS_bug_fix_v2.0-beta.md with the
version-agnostic docs/macos_download_fix.md; update README and install.md.