chore(docs): removal of deprecated contribution guide placeholder - #400

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: actions/setup-go@v5, jaxxstorm/action-install-gh-release@6096f2a2bbfee498ced520b6922ac2c06e990ed2, pulumi/actions@v6. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/