docs: introduce Duckmind and simplify the README - #2

Process completed with exit code 1.

MINISIGN_DEV_SECRET_KEY is empty or unset — refusing to publish unsigned artifacts

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: actions/cache@v4, actions/checkout@v4, mlugg/setup-zig@v2. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/