Add changelog entry for Python library docs

[paarthfern]

Summary

Adds a changelog entry (2026-03-02.mdx) for the Python library docs feature in the Docs product changelog. The entry describes the ability to generate Python library reference documentation from SDK source code using fern docs md generate.

Tagged as api-reference and configuration. Vale linting passes with no errors or warnings.

Updates since last revision

• Added CLI commands and usage details per reviewer request:
  • Full docs.yml configuration example showing libraries config and library navigation item
  • fern docs md generate CLI command
  • Brief explanation of what the command does (server-side parsing, local MDX generation)
• Removed _navigation.yml implementation detail per reviewer request

The config structure (input.git, output.path, lang) was derived from the CLI source schemas (LibraryConfigurationSchema.ts, LibraryReferenceConfigurationSchema.ts), not from an existing published example.

Review & Testing Checklist for Human

• Verify the docs.yml configuration example is accurate — the structure was inferred from CLI source code schemas, not copied from an official example or existing customer config
• Verify the feature description and workflow accurately reflects what shipped (sourced from CLI changelogs 2026-02-06 through 2026-02-13)
• Decide if a "Learn more" link should be added — no dedicated docs page for library docs was found in the repo, so one was omitted
• Preview the rendered entry at the preview URL and confirm formatting looks correct

Notes

• Requested by @paarthfern
• Devin Session

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[github-actions]

🌿 Preview your docs: https://fern-preview-1ac7dbfe-a238-4740-896e-b52190fb5a7d.docs.buildwithfern.com/learn

Here are the markdown pages you've updated:

• learn/docs/changelog/2026/3/2