docs: exhaustive usage.md — document all CLI flags, config keys, and GitLab CI/CD snippet

[Copilot]

docs/usage.md was missing most CLI flags and config options. The README duplicated what little was there, creating a maintenance split. This PR makes usage.md the single authoritative reference and points the README to it.

docs/usage.md

• New CLI sections: --skip-somef, --verbose, --threshold, --generate-codemeta, --notes-output, and all output-path flags (--somef-output, --pitfalls-output, --analysis-output) — each with a runnable example
• Output paths table: consolidates all four output flags with their defaults at a glance
• Version discrepancy notes: explains the note-vs-pitfall threshold with a sample notes JSON and corrected boundary examples
• Multiple-URL input: documents passing several URLs directly on the command line (without a JSON file)
• Config section: adds active_profile key, rsmetacheck.toml (no-dot) as an alternate auto-detected filename, and a complete TOML example covering all supported keys
• GitLab CI/CD: adds an explicit snippet for the recommended GitHub-token variant alongside the minimal one; fixes RsMetaCheck → RSMetaCheck capitalisation

README.md

Replaces the duplicated Usage section (CLI details, CI snippets, config examples) with a single sentence linking to the ReadTheDocs usage page — one place to maintain going forward.

[vuillaut]

@copilot rework the documentation (README and usage.md) to have a single reference to point to where everything is explain (usage.md) and in readme just mention usage documentation and refer to it.
This way we have a single location in the documentation to maintain.

[Copilot]

@copilot rework the documentation (README and usage.md) to have a single reference to point to where everything is explain (usage.md) and in readme just mention usage documentation and refer to it.
T...

Done. The README Usage section now contains a single sentence pointing to the usage documentation (commit docs: replace README Usage section with link to usage documentation). All detailed content — CLI options, GitHub Action, GitLab CI/CD, output format, and configuration — lives exclusively in docs/usage.md.