CARS-29382: fix documentation

[martin-dessureault]

What

Documentation Accuracy Audit for the car_req repository. This PR:

• Creates a comprehensive CHANGELOG.md with version history reconstructed from git tags
• Updates README.md with accurate version tags, complete options documentation, and fixes code examples

Why

Part of the Marketplace Documentation & Governance initiative (CARS-29216). The goal is to ensure all documentation is accurate, current, and aligned with Marketplace standards to improve clarity for engineers and LLM tools like Cursor.

Jira ticket

CARS-29382

Steps to Validate/Verify

Review the documentation changes:

• Verify CHANGELOG.md version links resolve correctly on GitHub
• Verify README.md code examples are syntactically correct
• Confirm all @schema options from lib/car_req.ex are documented

Additional Notes

Changes Summary

CHANGELOG.md (new file):

• Version history from 0.1.0 to 0.3.3
• Each version links to GitHub compare view
• Includes "Unreleased" section documenting this audit

README.md:

• Fixed installation tag: 0.1.2 → 0.3.3
• Documented all schema options (added: base_url, finch, cache, cache_dir, compressed, compress_body, fuse options, resource_name_override)
• Added :transient as valid retry option
• Fixed incomplete code examples (missing closing parentheses)
• Fixed typos: "recevies" → "receives", "thorugh" → "through", "af" → "of"
• Added link to ReqFuse GitHub repo

After merge checklist:

• Update version in mix.exs if releasing a new version
• Update CHANGELOG.md with changes
• Create and push a new git tag if releasing: git tag -a X.Y.Z -m "vX.Y.Z" && git push origin X.Y.Z
• Check GitHub Actions to make sure CI passes