docs: update README for v0.3.0

[brucearctor]

Updates README and .gitlab-ci.example.yml with v0.3.0 features:

• Install: nix, mise, go install
• Flags: --sarif, --incremental
• Env vars: SARIF_OUTPUT, REVIEW_INCREMENTAL
• CI example: incremental + SARIF artifacts

Summary by CodeRabbit

• New Features
  • Added incremental review support to GitLab CI jobs.
  • Enabled SARIF output generation and ensured SAST artifact publishing for security reviews.
• Documentation
  • Updated installation instructions (including Nix and mise) and revised the Install section.
  • Expanded CLI flags and environment variables documentation for --sarif and --incremental/SARIF_OUTPUT.
  • Added local SARIF example and updated CI/release examples to version v0.3.0.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Pro Plus

Run ID: 67b56fe9-d311-4eb1-9480-cc060b45957f

📥 Commits

Reviewing files that changed from the base of the PR and between ae59a45 and 4de8378.

📒 Files selected for processing (1)

• README.md

🚧 Files skipped from review as they are similar to previous changes (1)

• README.md

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📝 Walkthrough

Walkthrough

Changes

Incremental review and SARIF support

Layer / File(s)	Summary
GitLab CI incremental and SARIF wiring .gitlab-ci.example.yml	Review jobs now use --incremental; the security job writes gl-sast-report.json and always publishes it as a GitLab SAST artifact.
README usage and release documentation README.md	Documentation now covers Nix and mise installation, incremental and SARIF usage, related flags and environment variables, GitLab artifact publishing, and the v0.3.0 release example.

Estimated code review effort: 2 (Simple) | ~10 minutes

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately reflects the README-focused documentation update and version bump, though it omits the CI example changes.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch docs/readme-v0.3.0

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[coderabbitai]

Actionable comments posted: 2

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@README.md`:
- Around line 149-150: Update the README configuration table to document the
`INCREMENTAL` environment variable instead of `REVIEW_INCREMENTAL`, preserving
the description and default value so the documentation matches the
implementation.
- Around line 85-90: Configure the code-reviewer CI job to generate the SARIF
file it publishes by adding SARIF_OUTPUT set to "results.sarif" or passing
--sarif results.sarif to the code-reviewer command, while retaining the existing
SAST artifact configuration.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

---

ℹ️ Review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Pro Plus

Run ID: 8931c52f-fa5e-4e18-9712-1c4067b8170c

📥 Commits

Reviewing files that changed from the base of the PR and between f965f0c and ae59a45.

📒 Files selected for processing (2)

• .gitlab-ci.example.yml
• README.md