docs: update premium tier Docker instructions

[longieirl]

Summary

• Add docker pull and docker run example for the premium GHCR image
• Include volume mount flags (input, output, logs, license.json)
• Add license note: only required for credit card statements

Changes

• Updated premium tier section in README.md

Type

• Documentation

Testing

• Manually tested
• Tests pass (coverage ≥ 91%)
• make docker-integration passed locally

Checklist

• Code follows project style
• Self-reviewed
• Documentation updated (if needed)
• No new warnings

Downstream impact

• This PR changes a public interface in bankstatements_core