Mention how to get colors when building mkdocs site on ci

[sverhoeven]

No description provided.

[Copilot]

Pull Request Overview

This PR adds documentation explaining how to enable colors when building MkDocs sites in Continuous Integration environments. The change addresses a common issue where colors may not render correctly in CI due to terminal detection limitations.

• Adds a new section "Colors in Continuous Integration" with environment variable configuration
• Provides a practical GitHub Actions example for setting TTY environment variables

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