docs: make intro page follow Robert Ramey's guidelines - #397

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Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: actions/checkout@v4, actions/setup-node@v4, actions/upload-artifact@v4, alandefreitas/cpp-actions/boost-clone@v1.9.0, alandefreitas/cpp-actions/package-install@v1.9.0. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/

[sentence_length C2] sentence over 25 words (36)

[sentence_length C2] sentence over 25 words (27)

[sentence_length C2] sentence over 25 words (39)